Formula moms !

Okay so we started at similac advance , he stopped pooping at a week old , so we switched to nestle good start, but that didn't agree either , so we tried nestle good start dietary fibre , it worked for a week . Then he stopped pooping again . We had to stimulate for every poop Now we are on enfamil gentle ease it was a god sent for 3 weeks The. He didn't poo for 4days it was hard when he did and it hurt him . Now it's been two days so clearly it's starting agin ... I'm at a total loss of what to feed my poor kid :( he's almost 3 months and has had troubles pooping for his whole little life . What do you feed your little one ? Has anyone had this sort of problem and gentle ease not help?  What do I feed him ugh I feel so bad :(