You may have a food allergy. Try keeping a food diary. Limit the different types of things you are eating as much as possible and then every three or so days try and add something new and see how your body reacts or even take something out and see how it reacts.

You will need to put some thought into to make sure you are getting enough protein and such once you have enough information a pattern might emerge.

You may also want to include how much stress you are under in that journal as well since stress can affect your digestive syndrome.

Boiled rice and chicken breast are pretty easy for your stomach to handle, assuming you are not glutton intolerant of course. If you are having trouble with veggies try seeing if your body handles fruit OK.

Hope any part of that helps