My 16 Y.o. Son Has Been Sick For A Year

My 16 y.o. son has been sick for a year now. They have done a fundiplication for a hiatal hernia, thinking that was what was causing his pain and nausea. He hasn't gotten any better. They have done multiple tests. The GI came back with "There's nothing jumping out at me other than the lining of his esophagus, stomach and upper intestine are inflamed, so it must be gastritis" so she put him on 40 mg nexium a day. That is doing no good. What should our next step be?