My son had a severe reflux problem - he spit up after EVERY bottle for at least the first six months. THe pediatrician just said it was "his way". THen, he finally stopped and didn't start again until I started to wean him from formula and change to milk. THen, the reflux started again. My ped said - oh, he must be allergic - you should start him on Soy. Well, long story short is that I decided if he ahd gotten used to it once before, he would again, and I started him extremely slowly on the milk, and he did adjust. I would check any differences in your son's food, but also work with his pediatrician (even though mine wasn't much help).