Baby pooping less.

So my son is 6 weeks old and for the most part was consistently pooping 3-4 times a day. He is breastfed, but occasionally gets a bottle of formula. He eats literally all the time and has plenty of wet diapers, but seems to be pooping less. He stopped pooping overnight completely and has only been pooping twice a day the last half a week or so, and hasn't pooped today at all. Should I be concerned? I read that BMs can change around now, so just not sure.