Is this reflux or allergy?

My baby will be 6 months old on the 11th. He currently is on Enfamil Infant and has started to spit up a lot and has bellyaches pretty frequently. Sometimes his breathe will smell like soiled milk. When he was born he was breastfeed until I couldn't any longer (about 6 weeks.) And he was on Gerber Good Start but he just quit drinking it. I don't know if he just didn't like the taste or what. I put him on Enfamil Newborn and he did great but I switched him over to the Infant formula when he was 3 months. I've called my Dr's office and a nurse suggested alimentum formula but I really dislike Similac formula. I was wondering if I should try Gerber Good Starts again. Of course I'll do what's right for my baby...any suggestions? Anybody else out there with the same issue?