Newborns (1 week old) pooping


First time parents

We are giving our NB Similac formula, when we first brought him home for the hospital and started formula he pooped at least 3x a day, then around day 5 it was twice, day 6 &7 was once and day 8 nothing yet... just curious how often they should be pooping? He acts like he needs to usually by late evening, lots of grunting and pushing out his legs straight. He is passing gas fine but we’re not sure how often he should poop.