Baby waking in the middle of the night.

So my daughter is 3 weeks old. She goes down about 10:30-11 pm and wakes up between 3-4 am. I get up change her diaper make her a bottle and feed her. Well the last couple nights she spits up just about everything I feed her during her middle of the night feeding. Two nights ago she projectile vomited all of it back up. She doesn’t hardly spit up during the day. But then she’s just awake for hrs and it takes me forever to get her back to sleep... any thoughts on why she does this?