I have been in a simuilar situation to you for over 20 years. Not quite as severe but I would bet that my digestive permeability is greater than yours.
When you eat anything, as soon as food begins to break down in the stomach large food molecules, much larger than is supposed to enter the blood stream enter the blood stream within about one minute. I have itched within about 30 seconds of consuming anything which indicates the high permeability is present in the stomach rather than other parts of the digestive system as is commonly claimed. All the advice for leaky gut is WRONG! That is why it very rarely works.
A temporary solution, to strengthen your body is to use simple nutrients only which cannot cause an immune reaction. I would recommend getting some amino acids which should not cause any problems. Starting with a small amount of Branch Chain Amino Acids BCAA. This will supply essential amino acids Leucine, Isoleucine and Valine. Get a small amount from a body building supplier and see how you get on with that.
If that works okay, get the remaining essential amino acids. Getting some L-Cysteine, L-Glutamic Acid or possibly Glutamine and Glycine. These are used to produce Glutathione which should help with detoxification. You could get some Reduced Glutathione, a liposomal form might be best. This should help boost your bodies levels because vitamins/minerals are also needed to produce Glutathione which could be difficult to consume in the short term until your detoxification is working. Getting your detox systems working should be helpful and will hopefully allow you to supplement with important nutrients that your body has been mising. Glutathione supplementation would therefore be helpful. Once you have consumed that for some days, taking the needed amino acids for Glutathione production should help your body make some of it's own. Vitamins and minerals are also needed to produce Glutathione.
Your stomach function will be very poor and you probably have no active stomach acid. It might be worth introducing pancreatin after doing the previous steps and then try some oil/fat such as omega 3. Some lecithin would be helpful too, start small and work up.
BTW ignore candida, it is not your real problem, it is just an opportunist which people obsess over causing them to miss the real cause of their problems, a bacteria. This is what maintains the problem, treating a yeast when they should be treating a bacteria.
There will be biofilm(s) in your stomach which is likely to house the bacteria and also candida because candida can share a biofilm with some bacteria. From there it can seed the digestive system.
To successfully beat a biofilm you need to use quorum sensing inhibitors because I very much doubt that you will beat them without using QSI. My successes and I have not yet beaten it but have had some very strong effects in my stomach which approached a level I had when I destroyed a large portion of one of the biofilms, came when using QSI essential oils.
Using enzymes will help, Interfase+, biofilm Defence if I remember the name correctly, using separate serrapeptase and nattokinase which does not contain magnesium stearate because biofilms use magnesium, calcium, iron and any other metals. Some extra EDTA might help, large amounts can be kidney toxic. N-Acetyl-Cysteine might be helpful against the biofilm because it can prevent EPS production, aim for a minimum of 8mg/ml concentration. Large amounts of cysteine can raise homocysteine so do not go too high, it might be worth taking homocysteine lowering supplements before you start all of this but allow the stomach to empty.
Two good products for QSI are BFB-1 and BFB-2 which are complexes of essential oils. They need to be mixed with a good emulsifier, I am using the purest Tween 20/Polysorbate 20 that I could find. Avoid cosmetic grades because these are less pure and can contain harmful (cancer) substances in larger quantities than food grade or pharmaceutical grades. Tween 20 contains lauric acid which can also be a bit helpful but only tiny amounts will be used to emulsify the essential oil so the lauric acid is fairly insignificant. Mixing this stuff is difficult because of the tiny quantities, an ultrasonic cleaner would be helpful.
Be aware that if you have not been eating protein then your body will be producing large amounts of cortisol to break down muscle to provide needed amino acids for your body to function. This is very weakening on your immune system and body which is why I recommend taking amino acids to help stop this. Separate amino acids are a fairly expensive way of getting protein but it does remove the chance of immune system reaction. Getting some of the none essential amino acids would help reduce your livers burden, look at the ones commonly present in food and try and include as many as you can, especially those which are needed for important body processes such as detox. With leaky gut your liver will be working very hard to attempt to remove all the toxins flooding into your blood stream from your digestive system. It's only by defeating the bifilms in your stomach that you will eliminate the "leaky gut". It will also fix your colon as the stomach and colon are linked by the nervous system which is affected by these infections.
Bananas are very high in carbs, starch for less ripe bananas BTW so I cannot understand how you can eat them and not eat other carbs. Taking anti inflammatory substances might help, things like Grape Seed Extract, the powder tastes bad BTW because it is high in tannins and has a horrible mouth feel. Astaxanthin might be helpful, 12mg capsules are available. Reducing inflammation would be helpful because it can drive up cholesterol and many additional inflammatory markers.
If you are reacting with IgE antibodies, like I do, then supplenting high dose vitamin B12 might be helpful as it up-regulates T suppressor Cells which should help to reduce immune reaction. I was taking 30mg/day which allowed me to eat more normally. What I did not know at the time was that such high doses increases the need for Vitamin K and I should of taken a large dose of vitamin K2. Long term there can be negative effects on the circulatory system taking such high doses without vit K. I was taking some vitamin K2, by Life extension called Super K but I have since found out that it is not very bioavailable as shown by two independent tests because it contains mainly cis form rather than the active trans form. Finding a high dose of trans form K2 would be helpful in preventing calcium going to the wrong places such as the circulatory system and instead keep it going into the bones and teeth. Since I have altered this things have improved a bit with regard to the calcification of my circulatory system. At one time I was noticing a sensation when I breathed deeply which I believe was due to calcification of the arteries in my lungs. That has since disappeared.
There are different forms of vit B12, avoid cyanocobalamin and go for a combination of methylcobalamin, hydroxycobalamin (there are liposomal forms) and/or adenosylcobalamin. Methylcobalamin tends to short circuit normal processes so do not take too much, hydroxycobalamin keeps things working better. Folate, P-5-P (vit b6) will be needed and so will other vitamin B group, particularly B2 (R-5-P).
Try and get some glutathione into you and then move onto essential aminos with the Glutathione aminos and then followed soon after by some vits and mins, particularly magnesium. Once things are working a bit better you can attempt to destroy your stomach infection which should eliminate the cause of your problems.
Due to the extremely high detox demands placed upon your body and liver, your nutrient requirements will be very high and I doubt that you are getting any where close to sufficient with such a limited diet. Rather than the tiny amounts of many B vitamins, more like 100mg is likely to be needed. Choose the enzyme activated forms so as not to burden your liver which has other more demanding priorities. Check out methylation as it can be problematic supplementing for some people with certain SNP's. It can be difficult for many people getting this correct especially with some SNP's. 23andme could determine any weaknesses and all you to work around them more effectively. Fixing your digestive system is your ultimate goal after you have got things working a bit better. Candida does complicate things but do not fixate on it because it will lead you in the wrong direction and like many on this forum you will fail to beat it if you focus on the wrong thing.