When you have some kind of reaction to something but you don't know what is causing it, you can eliminate everything except something basic - like brown rice. Eat that for a few days, and let your body adjust to that. Then add some other food to see what reaction you get. Then later add something else, etc.
I've never had to do that with food since my body likes it all. But I do have to do that from time to time with people. I'm in the middle of an elimination diet as far as communication lines go. You know, if it's not working, sometimes it's just better to let it go and see what else is out there.