Sign of sleep regression?

My little one is 4 months on the 26th. But for the past few days she has been fighting her sleep and been extra fussy. She used to be down by 9:30 pm now she doesn’t sleep until 11:30pm -12am 😭 and within 9:30 to whenever she wants to sleep she is very fussy. Once she’s down for the night she’s done, she’ll wake up once at around 6am for a feed, then go back to sleep. I’m hoping it doesn’t get any worse. Does this sound like sleep regression?