changing formula?

ok so my 2 month old was first on the regular yellow enfamil and now she's on the gentlease one because she was very gassy, having stool trouble, and very grunty and always straining. now that she's on the gentlease she's still straining and grunting (not as much but still) and not always has bowel movements when she's straining and grunting, still gassy and now she has VERY WATERY poop. its dark green. i got a picture off the internet cus i dont have one but this looks exactly like it. any recommendations on other formula? she doesnt have AR she only spits up rarely when i she isnt able to burp. i dont know what other formula to try ive read to just try and try formulas until you get to the one that fits your baby but advice doesnt hurt