Waking up at almost the exact same time every night

My 8 week old baby has been waking up just after midnight everyday for the past two weeks or so. Sometimes she wakes up screaming. Sometimes she’s mellow so I’m able to change her diaper and feed her but eventually she’ll start her crying and screaming as usual. It’s so hard to put her back to sleep after she’s calmed down. She’ll stay awake for 3-4 hours before finally sleeping for 3 hours straight. I can’t figure out what the problem is. I’m worried she’s not getting enough sleep.