Based on my own experience, I would also suggest you try giving your son probiotics and yogurt (if he's not dairy sensitive). And ease up as much as possible on refined sugars. It sounds like he may have an overabundance of yeast in his digestive system right now. I'm not a doctor or anything like that, but I struggle with system wide yeast infections, my body is just very sensitive to pH changes and bacterial levels I guess.
Did your son by any chance just go through a course of antibiotics in the past few months? This is a big one that can cause major yeast problems. I just get destroyed by antibiotics, it takes at least 2 weeks for me to get my yeast under control again, especially in my stomach.
Think of what yeast does to bread, it fills with gas and rises. Same thing in the digestive system I guess. Whenever I have yeast problems, I start burping like crazy. Embarrasing to talk about this on a forum, but hope it helps you with your son.
Also, I agree with the other lady, don't give him Tums and all those stomach acid things, they are really bad for you, but I think gas-x is okay if it helps (it's not the same as stomach meds). If he has acid problems too, try magnesium supplements, it's a natural antacid and doesn't come with all the side effects of the over the counter and prescription meds for acid reflux. But it doesn't sound like your son has acid reflux, just sounds like yeast.