Gastritis for 6 months, what's the next step

I am a 27year old male, underweight, exercise frequently, with what I thought were healthy eating habits, and have not ever in the past had any health issues. Starting 1 year ago; occasionlly I would start to feel a bit nauseated but it would pass. This happened maybe once every two months or so.  6 months ago I became sick, with what I thought was food poisoning (but never vomitted or had diarrhea).  This time the sick feeling didn't go away, my description of it is a low level nausea and an ache in my stomach when I eat certain foods. There are no other gasto symptoms, for example no diarrhea, no painful areas of my abdomen. The doctors I went to labelled it gastritis and I went on omeprazole. The omeprazole appears to help, not completely, but it does seem to improve my symptoms. When I try to come off of it, I feel ok for the first day, but after that I start to get nauseated again. my stomach aches and I have to take it consitently for a few days to get back to square one.  I assume that I can't stay on omeprazole for the rest of my life, and it worries me that 1) there is some potential underlying cause not diagnosed 2) that I am slowly getting dependant on acid reducers.  I don't take any other meds; I don't take nsaids; two separate h pylori tests can up negative; don't drink alcohol anymore; rarely have any caffeinated beverages; endoscope didn't reveal anything; abdomen ultrasound didn't show anything, B12 levels came back ok, nothing showed up in blood work CBC.  My question is, what do I do next? This is such a strange problem to come out of the blue, and where previously I could eat as I pleased without any issues, now I live like a monk and still feel sick.

[CalGal]

One of the things that helps some with gastric issues is changing their diets. Have you considered doing trying that since you say some of the problem seems to be caused by eating certain foods. You may also want to consider having food intolerance testing done because some cases of gastritis and digestive issues can be caused by food allergies and intolerances.

When you want to come off the PPIs you're going to have to do it slowly and step-down in dosage over a fairly long period of time - weeks-to-months. There's a nasty little side-effect of PPIs - rebound reflux.