My 3 month old suddenly keeps waking in the night

Since 6 weeks my baby has been sleeping from 12am-7am in one go. She would wake up at 7 half asleep for a feed and go right back down for a few hours. (She wouldn’t even cry, I would wake from her tossing.)

Now she’s 12 weeks, and we were told by Dr to start instituting earlier bedtime, so we’ve been bringing it up 15 mins or so every few days. It was working fine but now, she goes to sleep at 10-10:30pm, and will wake up screaming at 5:30 (almost on the dot, every morning). I give her a bottle, put her back to bed and then she will wake again at 8 screaming as well. Sometimes she adds a 3am feed just for good measure.

I’m really not complaining, bc I know this is not a terrible sleep schedule for this age, but I’m wondering if there’s any tips on how to get baby to fall asleep for longer again? Or is this just how it will be?

I thought the older the get the longer they sleep through the night in one shot..