Formula help ☹️

So I believe my 6 week old has a sensitive tummy and acid reflex or some sort of reflex issues. She was on enfamil newborn and was switched to gentlease didn't seem to work for tummy issues so I switched her to gerber smoothe and now shes constipated but helps with everything else!! I have no idea what to do!! I can't afford to keep buying different milks and waste them and I just want her to feel better but It seems like I'm dammed if I do and dammed if I don't