Breastfed newborn not pooping

My 16 day old son hasn’t pooped in 6 days. He’s breastfed and I’ve pumped a couple of times to give him some extra and encourage more milk production. I’ve read that breastfed babies can go a long time without pooping but I’m starting to panic. He’s gaining weight and is almost back up to birthweight. Has anyone else had a similar experience? He seems like he’s getting enough maybe but not extra to poop out? Any advice or personal experience stories would be greatly appreciated!