Hello A....I am new but I know quite a bit about Acid Reflux in babies...2 of my children have it and see a Ped GI to control it! Couple questions does your son act like he is in any pain when he spits up(ex. arching his back, screaming for hrs)? All babies have some amount of reflux, just like adults! It's great that he's doing well weight wise but other things you need to look out for are signs of pain...untreated reflux can cause erosions and irritation of the espogus(sp?)among other things! Has he ever had any tests for the reflux (UGI, PH Probe, Endoscopy)? Is he congested alot of the time or is he ok in this department?
Couple of things you can do at home is make sure he is at a 30 degree angle when he sleeps at night(prop the top end of the crib up with a pillow(under the matress) Try not to feed him right before bed! Have you tried Alimentum...it worked wonders for my youngest and he had been on so many(Prosobee, Nutramagin, Neocate-this one is rx only, and then finally Alimentum! Also have you started giving him cereal at all...it sometimes helps to thicken the formula, but it can also make your child constipated! Also if he is in any kind of pain see if the Ped would want to rx Zantac...there are several meds out there but this is usually the one they rx first! Also the meds will not stop the puking but if your little guy is in any pain something like Zantac, Prilosec, or Prevacid are something I would ask your DR about!
I am absolutely no kind of expert...but these are just some of the things I have learned and experienced with my own child!