I am sorry to hear about your troubles. I myself have given up on the vegetarian option due to the inability to digest most vegetables and many fruits, especially high-protein legumes. Nowadays I eat a ton of yogurt and source all my meat so it comes from happy animals raised sustainably and organically and killed humanely. But good for you for continuing to give vegetarianism a shot. The problem with recommending specific diets is that everyone’s body reacts to stuff differently, and even digests at different rates. Here is some of what I have discovered works for me through years of trial and error:
Eggplant does not seem to ever cause problems, and has become my primary staple vegetable.
Asparagus seems to be safe.
Root vegetables are always a good bet.
Tomatoes are ok as long as I don’t eat too many.
No legumes, ever. Not even peanuts. I have heard that tempeh might be safe because it is prepared differently than tofu, but I’m too scared to try.
No broccoli or cauliflower.
No cabbage or brussels sprouts.
Onions, especially raw, are problematic. Same with bell peppers, though the greens seem to be worse than the colored ones. Chilis can be quite harsh, but I can get away with a de-seeded, sweet jalapeno every so often.
Melons can be problematic, except for watermelon which seems to be fine in reasonable amounts.
Apples are no good, unfortunately. I miss them.
Berries seem to be ok, as do bananas.
Leafy vegetables are ok in general, including leafy spices.
Everyone says to avoid whole grains, but I have been cautiously eating them recently and I think they’re ok.
Don’t just assume you have a sensitivity to gluten – have you had a Celiac test? I know some folks can still have trouble with gluten and not have Celiac, but that’d be the place to start.
Does your GI’s office have a nutritionist you can request a consult with? If not, ask to be referred to one. He or she will be able to help you with suggestions and tracking the effect of different foods. There’s a thing I’ve been wanting to try when I find a good nutritionist where you “blank slate” your diet by eating only rice for a week, then adding foods one at a time to see what happens. I haven’t tried it yet only because it sounds dangerous without medical supervision.
Here is a thread I asked about the same topic several years ago.