2 months old not pooping

My baby just went through that at 2 months. He pooped A LOT on day 4. As long as poop looks normal and it's not hard constipation like poop it's fine. Their digestive system is changing around this time and for some babies they use up all the energy in the milk that they start to poop less, for some they just accumulate for days and release it all when they're ready. Babies are generally very fussy around 2 months, peaking from around 6 to 8 weeks and it slowly gets better. If you're concerned about the pooping you can try doing more tummy massage and bicycle his legs regularly. Another method is rectal stimulation which can be done with just some vaseline and a thermometer. This can help them pass gas and poop quite effectively, but not really recommended as they might start relying on that rather than slowly learn the proper way from what I read about.