Baby not pooping

Elyssa

So we were having issues with a bit of reflux and some mucous in his poop thinking he had some sensitivities. All of a sudden he’s stopped pooping. It’s been 4 days now and normally I’d be freaking but his stomach isn’t hard and to be honest he seems more at ease than ever 🤷🏼‍♀️ we EBF and I have read that once babies stomachs mature enough they can go up to a week. Anyone else experience this at all? When is too long?