I hope that the doctor can give you some answers. Definitely sounds like something going on with the stomach. Are you going to have your doctor test for H. pylori?
In the meanwhile, you might try the
Specific Carbohydrate Diet intro diet. I did this when I wasn't feeling well myself. I would make a big pot of the chicken soup (recipe on the link I provided), and eat that all day long with jello. Make the jello out of unflavored gelatin flavored with unsweetened fruit juice. I think I'd stay away from the dairy for now, as well as the nuts. An elimination diet sounds good too.
Have you considered taking your son to an acupuncturist? I have a feeling that would be more beneficial than giving your son medications. My acupuncturist, who I'm working with on my food allergies, told me that antacids are about the worst thing you can take and most people do not need them.
Claire