Have you tried a low carb diet, eliminating Sugar and alcohol as well as fruit and starchy vegetables? Have you tried eating raw ginger, cayenne, and garlic? Your problem might be due to candida overgrowth, or perhaps insufficient stomach acid.
You could try a rotation diet, eliminate a certain food or group of foods for a week, and see if you notice a change. Many are sensitive to wheat, but corn, soy, peanuts, and other grains and legumes also cause problems for many. Do you eat beans or raw vegetables? Some people have trouble digesting those.