likely a developmental thing - babies will wake up early morning after x hrs asleep to play, to just be up, sometimes (like mine!) to do tummytime

- their brain is developing and they are wired to move or to be up as a result. you can do a lot to try to make things better but some of this falls under regression - there isn't much you can do as it's a phase. every kid is different so it's hard to know for sure but A LOT (according to the pediatrician) are like mine (and yours)

good luck!
DD wakes up promptly at 4am. i've tried bedtime at 6, 6:30, 7, 730 - does not matter. she goes back to sleep from 5-6:30 then. at 4 months she used to wake up at 3am and be up for 1.5hrs!! there's nothing i could really do since she was not fussy as much as up and talking and just done with sleep for that time frame..