Leaky Gut is what causes allergies because the digestive system should not be able to absorb large food proteins unless the permeability increases.
Not breaking down food properly in the stomach should not lead to allergies because the digestive system should not absorb larger food molecules. That is unless the digestive system becomes more permeable ie Leaky Gut.
This would explain your tiredness because Leaky Gut does tend to stimulate the parasympthetic nervous system and you get a thicker tongue coating. A tongue with little coating indicates sympathetic nervous stimulation the opposite to people who are tired.
Re: your blood pressure. Doctors and nurses rarely comment on lower blood pressure. They will only usually comment on high blood pressure so do not assume that it is not low just because no one mentioned it. Next time ask or look for yourself. Chances are it is not low because that would indicate other things. It's just the hair loss and lymph swelling which made me ask.
I had an allergy test which at the time made some sense but it was not until years later that I put all the pieces together and IIPS aka Leaky Gut was an important issue. Since then I worked out what caused that. I recommend that you do not dismiss it because you could find that it does apply. Just bear it in mind.
I keep forgetting to mention this so I will throw it in here. Soup stock made from bones and cartilage etc is regarded as very healing for the stomach due to the amino acid profile of the meat/bones. It's high in glycine which is very beneficial. Recipes are on the net for soup stock and the GAPS diet also recommends it for healing the stomach and digestive system. It won't help on it's own if there is any pathogen causing Leakyness or hypochlorhydria but it could prove useful to you. You could add herbs to stimulate your digestion such as Cloves etc to increase stomach acid production.