Adjusting to formula after breast milk

Formula feeding mamas, how long did it take your little one to adjust to formula if you switched over from breast milk?

My son is 3 months and we just switched him over a few days ago and he’s having trouble pooping. He did poop a little and it’s not constipation but he’s really not going much. The pediatrician wants to wait it out a few weeks to give him time to adjust and I’m just wondering if others experienced the same and how long it took to adjust? Did you have to try several? We are starting out with Similac Pure Bliss.