Best formula

So my 2 month old is very gassy all the time and hes been constipated alot. He is mostly on formula now and gets the boob a couple times. His poops are now smelly and green when he does poop. That's about every other day. So I thought maybe I could switch formula and maybe that would be better on his tummy or is it even a problem? He take gerber soothe right now. Hes fussy a lot but I dont think quite colicky. I tried gas drops but his belly still seems to hurt.