Formula Question …

How did you know your baby needed to be switched from regular formula to gentle ease or lactose free formula?

My 3 month old seems very uncomfortable after he finishes his bottle… he grunts, whines, whimpers, and sometimes screams like his belly hurts. He’s gone from pooping multiple times a day to pooping once a day to going two or three days without pooping. And the consistency of his poop has changed from mushy/runny to solid/mushy. He doesn’t act like this after every bottle, at night he drinks his bottle and falls right asleep no problem but during the day his bottle seems to really upset him.

I’ve brought this up to his pediatrician multiple times and he says it’s “normal” and his digestive system is still immature and he has to “suck it up and learn how to poop”

Could it be gas or colic or the type of bottle we use? I’m not really sure what to do… any advice is appreciated.