I am 75 years old, but I have gerd reflux too! I can not eat uncooked fruits and vegetables, especially meat, when it is tight---when I am nervous or stressed--as it gets "caught" and comes back up, usually after much painful wrenching, until the troublesome piece, or pieces, comes back up, then instant relief, but if I strain much to vomit and get the substance out, yucky mucous builds and comes up---several times, usually-- I am incredibly tired and do NOT want to eat for while as my body just isn't ready to "try again". If your son has had many of these episodes, I can understand his reluctance to eat--anything--his not knowing what may trigger some of these painful episodes. I realize I am older, but my Dr. told me to stick to puddings, or liquid things that will slide through more easily. I, too, am on meds, and they usually take care of it--before hand, DON'T try to take anything if it is actually into a "reverse" situation as that makes it MUCH WORSE!!!
I am now on Prilosec, over the counter, was on Ranitidine, but it got so it wasn't strong enough.--
I would just let him pick and choose soft foods, that he feels like he can handle as it is impossible for someone else to determine that, but try to cook foods, not give fresh, uncooked fruits and vegs, and especially meat, until he gets over the memories of these painful incidents, and I feel that he will gradually begin to sample other foods, especially if he sets at the table with the rest of the family and watches them eat, it is hard to resist doing what others are doing---give him time as I know, from experience, how traumatic these spells can be---and it takes time for the unpleasantness, associated with eating, to fade.
Best of luck!! PR