Days without poops

Bry
Babykins is strictly formula-fed. Never had any breast milk. In the beginning, she would poop like six times a day, but now will go two or three days with no poops at all. The doctor at the last appointment asked if she poops at least once a day like he would be content with that. Then the very next day she stopped pooping. Anyone else's baby do that? Is it okay?