My son had GERD too. That could be the case with yours, but the time I remember from when he was really little and he threw up bright yellow bile, it was after he had thrown up everything else in his stomach. It turned out he had an ear infection. Absolutely no other symptoms other than vomiting. If you haven't brought your baby in to see a doctor yet, I would suggest doing that, since they can check for things like ear infections so easily. Even if he has no other symptoms I would still go and have his ears checked out.