I am sorry about your boy. I am really, really opposed to the use of Zantac and like medication in babies. I hope the GI can help him in some other way. I have had reflux since I was 14, been on so many different medications for it and the only thing that actually helped was removing certain things from my diet, which I didn't learn until 5 years ago. My best friend has a baby with it as well, and since she is Celiac with Crohn's, which are serious digestive disorders, they watch him very carefully. The Zantac worked for her son for about 2 months (they started him on it at about 2 mos. old like your boy) and by 4 months it was pointless. (you also should watch out b/c most GRD drugs are actually not approved for infant use and the two that are were only approved VERY recently.)
My best friend is breastfeeding her son and decided to try changes to her diet. She is the one who introduced me to the special diet several years ago. it is called the "specific carbohydrate diet" and the book is writeen by Elaine gottschall. with all the talk of carbs lately it sounds like a weight loss book, but it's not, it is a special diet designed decades ago to help people with severe digestive problems. My friend and I personally use the diet anytime we have bad flareups--and it gets us through without medication or surgeries. I have had one surgery and she has had two. I am currently medication free and she is down to one med. Doing the diet for her son helped his tummy, and he currently does not take a GRD medication.
I want to give you better advice than that but if I knew I'd have to be a GI myself. Consider getting this book from the library and reading through it. this is just what worked for us.
-C. G