Gas generally comes from some sort of fermentation or rapid oxidation so something musta become dislodged and while making it's way out it was oxydating rapidly and causing all the gas not to mention that it's prolly toxic matter also thus making you feel sick and nauseous. You mention having done the BP shakes during your juice feast. The BPs are great at what they do but on a juice fast not having other solid matter to help push it out they can become very dehydrating not to mention absorbing a lot of the nutrition from what ever juices you are drinking unless you are very judicious and only do them one hr before or after your juices and then on top of that you hafta drink lots and lots of water because both of the highly absorptive nature of the B&P and to keep things well hydrated to push the stuff out. I mention all this cause if you weren't very judicious as I mentioned before according to Andreas Morrits the B can become plaster like when doing a liquid fast and could very be that you might have formed some kinda small blockage and you just turned loose some of it. Now all of this is simply an educated theory it could just be plain ole detox.
Having said all that the real issue at hand is to get you back on track and the first line of defense is always to up your liquid intake significantly to make sure you are well hydrated and the system is not trying to hold on to all fluids and to keep any toxins diluted and moving out. You can also try cutting back on the cayenne. That stuff is pretty powerful at dislodging mucous/toxins which is a good thing but when more stuff is getting loose than the system can handle it overloads the system with toxins and you can a have a Herxheimer reaction from too many toxins released at once which can make you feel ill nauseous and make you wanna hurl. If you are not really well hydrated it can cause the dry heaves.
You're already hip to doing the water 30 mins pre SWF so keep doing that and just significantly increase your fluid intake both water and lemonade and see how it goes. At least for me and in many cases that have been discussed here the SWF can take 1hr to 1.5 hrs before starting to go through you so empirically that seems to be a norma thing. The other thing I do is if by 1.5 hrs I don't have any out put or significant output from the SWF I'll chug a qt of water.
The MC is also considered a kidney cleanse so it's pretty common to have discomfort there. I suffered from kidney stones pretty bad to the point of being hospitalized a coupla time till I started doing my annual 40 dayers. Now that I mention this one the indications I would have when stuff was beginning to get loose in the kidneys was nausea and my body going into evacuation mode out of every orifice. Is there wasn't anything to vomits or poop out I would just get the dry heaves and stomach cramps so you might have loosened some sediment in your kidneys. Just to reiterate the issue now is to get you back on track and the first line of defense is to increase fluids
The hardest thing about exercise is the getting started part and even once you get started will be the initial struggle to get past the muscle aches and pains till you feel comfortable and seeing those result. I promise you it will be well worth any of the effort energy you put towards it. It will be the fastest most efficient way to see those changes. Not just physical but clarity of thought and attitude. The fastest regiment that will give you results is weight or resistance trining. For the not so dedicated folks with busy life styles there is something called Slow Weight Training. If you do it right and don't cheat you ony hafta do it once or twice a week. An easy read book on this is called "The Power of Ten" by Adam Zickerman. I'm not sure if the name or spelling of the authors name is right I'll look for my book later and correct if different.
I'm sure that you can do some herbs to continue support for the kidneys but anythng in the 3 week range of MC will do a pretty thourough job. The best thing one can do unless you have specific issues that need further cleansing is to drink half your body weight in oz of H2O. For example is you weight 120 lbs you should be drinking 60 oz of H2O daily.
There is a time factor in f or cycles when fasting that can't be compensated by doing more lemonades. There is a very informative post in the FAQs at the top of the page that I posted long ago called Detox Stages. This will give you a relative idea of the fasting time line. If you continue post MC with juices you will still continue to detox albeit at a slower rate but you will be infusing your system with some readily assimilable mega nutrition including vitamins, minerals and live enzymes. This has become my standard routine for the last 3 40 dayers I've done. At least 21 days MC then switch to green juices for the remainder. Love it!! the feeling of well being is fantstic!! I'm currently waiting to finish a project to start a much needed cleansing routine.
On the longer fasts including if you switch to juices you need to take more time breaking the fast than that outlined in the MC book. You should take a good 7 10 days breaking the fast. Wait till you're back on solids and having regular eliminations before doing the liver flush. This allows the system to build up some bile and you'll have a more productive flush.