Have you even been tested for parasites? Most main stream doctors or labs don't test for everything so some get missed - maybe a good 3 month of a parasite cleanse would do you some good. And good health food store can tell you what to take.
I'm on day 3 of ZERO carbs. All I've eaten is meat/eggs/fish. Strictly protein and fats. NO dairy of any kind, and absolutely NO fruits or vegetables. I'm going to keep this up for 2 weeks. Day 1 and 2 I had the typical tummy troubles, but much less diarrhea on day 2. Day 3 has been NO tummy troubles and NO diarrhea - so I'm hopeful that I'm on to something here.
Lets stay in touch and see if we can help each other find the answer! You're welcome to come on over to my journal.