How do you know if its colic or reflux?

My child is now 4 months. He has cried and cried since the first day we brought him home from the hospital. I had to supplement with enfamil lipil, that was horrible, so I switched to A.R and constipated him, gentlease, soy, alimentum, which didn't really help but made him vomit even worse, then nutramigen which also came right back up, then similac sensitive. He was projectile vomiting all the time so Dr. suggested upper GI which said he had a mild case of reflux. We are on prevacid, 7.5 mg 2x a day. I tried the reglan but it seemed to make him fussy so I dropped that. It just breaks my heart to see him in so much pain he tries so hard to be happy and will let a smile out every once in a while and it makes it all worth while, but for my own sanity I just hope it ends soon.He is currently on alimentum with 2 tablespoons of added rice and still vomits a little but not as much as it used to be. I haven't been able to go back to work because he is so sad so now my fiance and I are trying to manage on one income..so any advice would be greatly appreciated! Has anyone ever had trouble with the alimentum not helping or the prevacid making them fussy? thank you for listening? Does this end