Poop cycle

So our boy was born 05/11, he passed the “fudge” looking poop while in the hospital. Mom was breast feeding but was unable to produce milk. As of the other day, 05/14 we began feeding him formula. As of this morning, mom was able to product milk via pumping. The thing is he has only pooped once. I’m starting to get a little worried as he isn’t pooping. How long have some of you experienced your son’s or daughter’s going for a few days without pooping?