I need some mommy advice...very sick baby?

So I have been up ALOT tonight so if some of this seems a little like jibberish sorry lol. My daughter is 4.5 months old. She was 5 weeks premature but all in all a healthy baby when she came. She has been very fussy since birth and doctors have chalked it up to colic. Which I agreed with until recently. She was fed up until about a month and a half ago when my milk supply stopped. So we put her on regular formula. She couldnt keep that down so they said lets try soy. That didnt work either so finally we are on Nutramigen...also not working. Well she isnt as fussy with it but she is still throwing up most of what she is eating. I have even tried pedialite to keep her from getting dehydrated...no luck threw that up too. I am running out of options. They have her on prevacid for acid reflux. She has been running a fever intermittently for the last month and they dont have a clue what is wrong!!! Does anybody else have a similar experience or some sort of suggestion I am really worried about her she is already small and she is losing weight not gaining?