Should he even be on alimentum?

my son is 3 months old. when i stopped feeding at 1 month i put him on similac advance. he hated it. he would projectile vomit it and spit up large amounts after bottles. so i switched to isomil advance after about 5 days on similac advacne. he wasnt spitting up as much but his face broke out really bad and he was just as fussy. so after about 2 wks of misery on the isomil i tried the premade sensitive R.S. from similac and he did ok on it for about 2 days, then the **** hit the fan. so i read up on different formulas and decided to try the alimentum w/o dr. recomendation. he has been on the alimentum for about a 1 1/2 months now and since he has been on it, he has been WAYYY less fussy, he still spits up a little bit, but he developed acid relux and is now drops for it. its way to expensive, it smells horrible and it tastes bad. this past week he has started pushing it away like it was nasty. he would not eat much of any of it today so i made him a bottle of the similac sensitive powder(which is the only similac i have not tried yet) and he gobbled it up and liked it. im wondering if i should even keep him on the alimentum because i dont know if he even has food allergies and hes not even that fussy anymore. ADVICE?????