Formula switch

So I've been using gerber goodstart soothe for the past few months and I really love it but it's much pricier than some of the other formulas out there so I'm wondering how switching might go. I put him on it because he was very fussy and gassy and with regular Similac and Enfamil he wouldn't poop, I mean he'd go days, and if he didn't go at least once a day he'd scream. So anyway he's almost 4 months and I'm wondering if now that he is a bit older, if his tummy might tolerate a regular "gentle" formula. Has anyone switched? Does anyone feel like their babies tummies are stronger now?