Just something to consider...My son, who is 2 now, started spitting up around 3 weeks old. He would pretty much spit up everything I fed him. He was on breastmilk at the time. I tried soy milk, and all the different types of milk, at my Ped's request. Nothing worked. They treated him for Reflux, nothing helped. They guessed at Reflux, or allergies, etc. In about a week...he had lost over a pound, and was so weak he couldnt even cry. He hadn't used his diaper in so long, I was sure he wasn't even getting any nutrients. I rushed him to the dr's office, sat him up on the counter...without an appointment, and demanded to see a DR immediately. The DR came out, took one look at my son..and rushed him back into a room. Of course, it was a different DR than we had before. She pulled up his shirt, after feeding him some pedialyte...and we watched it bubble down his intestine, you could actually see it thru his skin....and then suddenly, it would convulse, and he would spit it up. They diagnosed him with Pyloric Stenosis. This is becoming more common in baby boys, and it's when the muscle at the bottom of the stomach closes...and doesn't allow food to pass thru. My baby hadn't had anything to eat for realisticly, a week. He ended up having surgery on the day he turned 4 weeks old. He still has a little scar on his chest...but he's grown to be so big! he's a very tall, fit boy for 2! I say have your peds do an ultrasound, just to be sure. I had someone suggest to me that may have been what it was when he first started doing it, and i asked my Ped about it, he said, no, that couldnt be it...so I just brushed it off. DON'T SETTLE FOR A HALF HAZZARD ANSWER! If that ped had performed an ultrasound that day...my son would have been in surgery that next day, not starving to death for a week!
Good luck, I hope you figure out something!