Not quite sure what to do...?

When my daughter was first born she was on enfamil lipil, and aftter 2 weeks she stopped pooping, had bad gas, and was projectile vomiting.. She was just miserable, I started giving her Nutramigen that a freiend had left over from her daughter, everything was fine at first, but now she wants to eat constantly, after every hour and a half to 2 hours, she is having gas, and is really miserable (it seems like she has a stomach ache). I want to try something else but not sure what to do... I was thinking of trying soy, I don't really know the difference between soy and nutramigen. Please help! Does anyone else have any expiriences with this?