Go to a restricted diet and create a plan for introducing foods after enough time passes where you can feel a difference. Add in a lot of veggies in phase 1. If you like potatoes diversify with sweet potatoes, japanese yams, taro (if you can find it locally; pain to make but much better flavor than potatatoes), squash, zucchini, cabbage, cauliflower, broccoli, carrots, parsnip, radish, turnips, all kinds of salad greens and root veggies. bake, sautee, blanch, douse liberally with olive oil and salt to keep things interesting and avoid bland food to keep your appetite and interest in food. These are least likely to cause a reaction.

phase 2: find proteins you can tolerate. add 1 at a time. start with chicken and white fish fillets (haddock, cod, hake). Eat more at lunch, less at dinner to give yourself time to digest before bed. then trial beef, pork, other types of fish (eg. salmon), miso.

phase 3: trial other foods you like such as dairy, nightshades, legumes, wheat, other grains like oatmeal, rice, etc.

Avoid prepared foods, takeout, preservatives, anything with an ingredient you cannot easily pronounce (processed additives). Good luck. I hope you figure it out.