I have acid reflux due to a hiatal hernia. Nexium is the best that I have tried. It is a prescription though.
A few tips for GERD:
Raise up the head of the bed. I use a sleeping bag folded up UNDER the head of the mattress. At hotels, etc. I put pillows or whatever I can find under the mattress. Don't just raise up his head with extra pillows (on top of mattress) because this will put too much pressure on his stomach muscles and force up the acid.
Avoid nuts, chocolate and mint. I switched to Tom's of Maine fruity toothpaste at bedtime. My GI doc said these things loosen up the sphincter muscle allowing acid to escape.
Don't go to bed or lay down right after eating. I try to wait 3-4 hours.
Carbonation is horrible for GERD. So is anything greasy or deep fried.
Eventually when I got a handle on my acid reflux I re-introduced all the above foods and everything was fine. I still do keep my head elevated.
Also, make sure he gets lots of water to keep him regular. Constipation stops everything from moving in the right direction and makes acid reflux horrible.
Good luck to your son. I hope he gets some relief!