Newborn constipation

Hi everyone, my baby is 12 days old and for the first few days he was pooping everyday about 3-4 times a day. Now, he hasn’t pooped since yesterday and seems kind of uncomfortable and fussy. What can I do that is safe to get him to poop? And is it normal for him to stop pooping as often as he gets older? We’ve been having trouble latching and getting milk supply up so I’ve mostly been doing formula... does that have anything to do with it? Is the formula hurting instead of helping??? I’m a first time mom so this is all very new to me 😰