So spoke with the nurse at the ped clinic and she told me to use rice cereal to thicken the nutramigen for today (my ped wasn't in) and if I want I can bring him in tomorrow and he can check him out and possibly give me a prescription for a thickener.
I am pretty sure that they tested his stools for occult blood while we were in the hospital, and there was none, so who knows!!
He weighs 5.2 kg, so he is getting a decent dose of the rantidine (10mg) as well as the Prevacid (10mg), so I doubt that he will increase his dose.
Fingers crossed that this will help my poor little refluxer!!
Thanks to all of you for your support and suggestions