3.5 sleeping help?

Hello mamas! Im a FTM and need some help decoding this. I know babies are forever changing but im so sleep deprived.

My 15 week old ( 11 week adjusted- born a month early) has been a great night sleeper. Down from anywhere 8-9pm.. Normally only 1 feeding. Wakes from 6-8 AM depending when she went down. Her naps were only 30 min intervals but she has a dairy allergy and im EBF and we think it was gas waking her up. That has been fixed.

She started cluster feeding about 8 days ago for a couple days and was napping for 45-50 min and at night sleeping a usual 7 hr stretch then after a feeding she literaly wakes EVERY HOUR. I was feeding every wake at first but now I just replce her paci and she is fine.

She no longer is cluster feeding and her daytime naps are still 50 min-1hr now but she is still in a night time funk.

She goes down 8-9 PM and will sleep abt 7 hours. We feed, change, swaddle paci and she goes RIGHT to sleep. When she is in a dee sleep she spit the paci out and this has NEVER been an issue. Ever.

Now when she wakes up to feed in the midde of the night i make sure she is getting full and relace her paci and she knocks out again but I was up an hour later to her grunting and whining with her paci out. I replace it and she is back to sleep again for an hour. And this goes on and on and on until its time to wake up. (She was doing this even when i was feeding at every wake)

Can someone give me some advise on whats going on? She was born early so i think we went through a growth spurt and we are done w a mental leap so why is this still happening? Isnt she too young for the 4 mo sleep regression since she was born early?