Because you seem to have had all kinds of diagnostic tests, and the doc has determined that nothing life-threatening is wrong, I am going to suggest some other ideas.
To find out what food allergies you might have, you would need to go to a doctor for skin tests. Actually, wheat is highest on the list for food allergies, eggs is also high on the list.... so instead of guessing it would be better to get the skin tests to find out for sure.
The next question is --- How long has it been since you have been on antibiotics? We know you had a colonoscopy. Both require rebuilding of the gut flora with probiotics immediately afterwards. So, ask yourself, did you do that? If not, then you probably need to rebuild the gut flora with probiotics no matter what is going on. Did you know that in Italy, for instance, no antibiotic are ever sold without probiotics sold along with it?
FYI: Here are a few of the kinds of foods that build probiotics in your system naturally: all fruits and vegetables particularly beans, asparagus, onion, garlic, bananas, artichokes, root vegetables, apples and pears. If you aren't a vegetable lover, you can probably buy dehydrated green superfoods (fruits and or veggies). You take a scoop daily in a small drink, or you can choose to take probiotics to build up your gut to a friendly environment and stay on them.... or you could do both for a little while and see how it works.
One of the first kinds of destructive organisms that takes over the gut after antibiotics and/or a colonoscopy when the gut owner does not intervene with probiotics, is a yeast called candida. When a person's gut is over run by this yeast it, interestingly enough, causes food allergies, sugar cravings, and pain -- so Paul, you can see how one thing leads to another.
Really brief and quick here: --- If you want to do probiotics get both kinds; the live kind and the other kind. Spend money for quality products. I doubled up on the 2 different probiotics when I had a problem. Also, I had a holistic doc recommend borage oil which is an anti-inflammatory some years back when I have abdominal pain and it worked.
If nothing works, go back to the doc.