help please!!!

Ok so my 3 month old has reflux and is on prilosec 2X day. She has been on Nutramigen since a month and a half. We tried to switch her to gentlease but she started spitting up A LOT before the switch she never spit up and now we are back on nutramigen it has been 2 weeks and she still spits up a lot.Has anyone else had this problem? Pedi is recommending we switch her to Alimentum but I don't want to keep switching her formula. Note we were never told she had any sort of allergy to milk or anything we were just told to try nutramigen to help with reflux.I have tried putting rice in bottle so thick its like gel and she still spits up.I guess I can live with the spit up but I really would like to know why she started spitting up and why it hasn't gotten better. Any advice or feedback would be appreciated