My 9 Year Old Has Had Stomach Pain And Nausea

My 9 year old has had stomach pain and nausea ever since a stomach virus he had 9 weeks ago. He's had tests done and determined it isn't celiac. He describes the pain at times as burning and just above the belly button. He's been on Zantac and Prilosec for 5 weeks which isnt helping. I can't pinpoint entirely which foods make it flare worse but know that tomato foods are a definite no like chili or spaghetti. I do notice too that stress will also make it flare up badly. We are waiting for an appointment for a scope to be performed and hopefully some answers.