Almost 6 months of this aghh

My diet now consists of chicken and lettuce sandwiches, no dairy, apples, bread, chicken salads, blueberry muffin, bananas and peanut butter. I'm meeting my needed calories a day, and I get really hungry at times. I just want to know if this diet sounds okay and hopefully at least some idea of when this misery may end, thank you.

There's a lot of information not given, eg, age, weight, sex, active person or not, food habits, smoker, etc. An endoscopy will only give so much information i'm afraid. If a sample was taken during the procedure it could have shown if you had H Pylori or something else. Had you had bloods taken or anything else done? 

Everyone has their own trigger foods with gastritis.  Keep a food diary to see if any foods are causing nausea and heartburn.  The key things to avoid are spicy, fatty and rich foods.  Omeprazole can cause mild nausea; I took omeprazole and had mild nausea from it which did clear after taking the medication for a while.

Did your endoscopy look for h pylori which can cause gastritis? 

Again, tests were negative as I said above, blood, stomach sample, etc, I'm 19 fairly active, male, used to smoke and drink but not anymore except weed