here are a few alternative perspectives to consider.
Your son may have swung from producing too much acid to not having enough. Hydrochloric acid (the stuff antacids and PPIs suppress) levels in the stomach are a main indicator to your LES ring that it's time to close. If your body does not produce enough HCL, the LES ring does not know that it's time to tighten things up and stays open. Moreover, we need HCL to properly digest food, absorb nutrients, etc. Does he have any abdominal pain, bloating, diahrrea, or gas? If so, try supplementing with a good digestive enzyme (the good ones have a diverse set of enzymes and although pricier, you will need less of them) at every meal. Try this for one week and see if he experiences improvements. If not, try supplementing with HCL and pepsin at one or two meals. He should know pretty quickly if this helps or makes no difference / worsens. If it makes it worse, he can simply discontinue.
HCL helps the body maintain a healthy flora. Your son may have an imbalance of intestinal or gut flora (bad bacteria generate hydrogen sulfide gas which puts pressure on the LES ring as gas pushes up). Put him on a good probiotic (3 before breakfast and 3 at bedtime). Try this for one week and see if it helps. If he still has gas and bloating even with the digestion enzymes and probiotics, try active charcoal tablets after every meal. They absorb excess acid and help the body eliminate toxins and pathogens that might have taken over his intestinal terrain. He should try this for 1 - 2 weeks and determine if it is helping or not.
Reduce the stress on his digestive system for a while by giving him steamed veggies (raw is too tough on digestive system), soups, oatmeal, and if he must have dairy go with goat milk or kefir (easier to digest). Beans, meat (unless light and in a in soup) and some grains are tough to digest so perhaps he can keep a mainly soup diet for a few days. Eat much probiotic and fermented food (yogurt, kefir, pickles, kombucha, seaweed).
Finally, if he is vomiting, his pylorus may be clamped up due to stress (most newborns spit up their food because their pylorus is still forming. Adults get similar symptoms but because of stress). The pylorus is a small muscle at the bottom of the stomach that opens when food is ready to pass to the intestines. When it is clamped up it stays shut and the food accumulates in the stomach. After a few meals of this, food fills up the stomach and your body tries to eject it because it has no where else to go but upwards when the stomach starts contracting to digest food. If you think this is his issue he can try a motility drug like Motilium 30 mins before each meal. He should feel relief by day 2 of this so it's pretty easy to check if this is his problem. Mobility drugs - like PPIs - are not natural though so they are not the optimal long-term solution. Most people I met that healed their GERD using PPIs + motility drugs were able to stop both medicines after taking mobility drugs for 2 months. If he still has issues and this is his problem, he may need to have his pylorus dilated. This procedure is similar to having an endoscopy and does not require surgery. I met a woman that suffered GERD for a decade before discovering it was due to her pylorus/stress. Vomiting/nausea were major issues for her. She has been pill and GERD free now for 20 years (she did the mobility drugs with PPIs and found relief. A few years later the GERD returned and she needed the dilation). Not many GI docs are familiar with this procedure so you may have to shop around for a good doc! In the meantime, ginger tea helps settle the stomach as does fennel (you can include it in his salad).
I hope this information helps and wish you and your son the best of luck!!!