Awake after night feedings!

The last two nights my 4 week old has been waking up after feedings at night and takes an hour to go back to sleep. I hold him upright for 20 mins after his burping and he is completely passed out and as soon as a lay him down he instantly wakes. I go to offer him his soother and he just spits it out so I try more milk and he doesn’t want any. He is formula fed as well he is on nutramigen. He just started doing this and it’s making me extremely exhausted. Any reason to why this could be? I really don’t want to bed share.