Baby not pooping every day: is it normal
This is very normal for babies under six months old. We breastfed, and I think for a while we were down to one poop a week! As long as your baby is producing enough wet diapers, is gaining weight properly, and is happy, then there probably isn't anything wrong at all.
My husband used to say that our daughter was just so efficient, she was using every bit of milk, and there wasn't any as waste. :)