Elemental diet - Being on this for 8 days reduced my reaction to normal foods (gluten, alcohol, ready meals & dairy based foods) considerably and normalised my stress response and improved BF by about 40%. I felt very calm and zen after and was MUCH better at handling stress because the stress tap wasn't on anymore. Eating "normal" foods for a couple of weeks made me go back to square one again though.
I'm sure you know that for many many people, alcohol, gluten, dairy, etc. are not "normal" foods. I'm guessing by "normal" you're referring to a time when you could eat these things and not have a reaction. You really do need to listen to your body - if your brain fog improved 40% by cutting these out, that's huge.
Having said this, one thing you might look into doing is a liver detox. My liver was seriously overloaded with toxins several years ago (it seems from exposure to chemical solvents from a job I had a long time ago) - one glass of wine would make sick for an entire day, 2 glasses would wipe me out for 2-3 days. I did a liver detox under the supervision of my chiropractor using Standard Process products, it took about a month and was kind of rough, but my liver was much better afterwards and I was able to tolerate alcohol again. I also started taking milk thistle for liver support.
Another thing you might consider is FOOD GRADE diatomaceous earth - not to be confused with the non-food grade stuff they use in swimming pools, which is not meant for human consumption. The DE can help with detoxing and killing candida and pathogens, and all these things can contribute to brain fog and may be part of your problem. I used to have a lot of problems with detoxing - even after doing the liver detox - my detox pathways just were not working right and then it seems through a confluence of 3 amino acids initially taken separately, many things that used to make me detox no longer did. these amino acids were glycine (which initially gave me a VERY strong detox reaction - I had to go very carefully with it), inositol and glutamine.
If you try the DE, go slowly as it can cause a detox reaction. The amino acids I mention above I think would help with any detoxing process, but again go slowly. But for years I would just keep reacting to things, and those amino acids helped me finally make some progress. Here's an interesting article about phase II liver detoxification, and it mentions these 3 amino acids, in addition to other important nutrients:
http://www.diagnose-me.com/treatment/liver-detoxification-phase-II-support.php
Also, I have read anecdotal reports about DE helping with food sensitivities, maybe from killing parasites.
Good luck!