Why is it that whenever I eat a banana, avocado, peanut butter, sunflower seeds, or salmon, my stomach BURNS ?

Whenever I eat any of these things, my stomach, within minutes, starts to burn and cramp. Its not like an, Ive got diarrhea type burn. Its like I feel like I must have an ulcer type of burn but only occurs with these or similar foods. Its gotten worse over the years. It used to just be eggs that made my stomach feel like this but now I can't even eat a peanut butter and jelly sandwich or guacamole! I've tried to figure out what all of these foods have in common...could I be allergic to omega 3's?? Would appreciate any insight. I'm frustrated and annoyed at what I can no longer eat. Its hard to "diet" when you can't eat eggs or half of the things that are great for you!