how often and for how long is a 4 day old baby supposed to nurse?

feed on demand! whenever they want and for as long as they need

so like 6 mins every 45 mins is fine? other then the fact that it hurts and I literally don't sleep she's okay?

sounds good to me. the guideline is every 2 hours but if she wants it more often thats great. shes building your milk supply 😀 I know it hurts, hang in there and use your nipple cream!