my son as well didnt used to poo until 5 days. we took him to the doc to get medication. after medication, still only poo after 5 days. then my husband read that some breastfed babies only poo once in 10 days!
he never had difficulty pooing. no crying nothing and he seemed happy baby.
anyway now he partially breastfed and formula. he goes poo once in 2 days