Formula help!

Long story short I started breast feeding but eventually i wasn't producing enough! I started giving my baby Similac for supplementing from breastfeeding. He was ok with it for a couple weeks then he started getting really bad stomach aches where his tummy would get hard. I have recently been using gentlease babies r us brand. And it has been doing good on his tummy. But I also tried the travel packs of the Enfamil gentlease and it seems when I use the Enfamil brand it gives him a tummy ache too. What formula would you guys recommend to try for my baby boy?