What is happening with my baby?!

T

My baby has gone from napping 3 times a day, albeit shortly, and sleeping all night to going into a frenzy each time we now try to nap her and put to bed. Once in bed at night she sleeps perfectly all through but the lead up to it and all naps has become horrendous. She stayed at my parents a few nights ago and got upset that night but I then got back to settle her ti sleep. It now seems to be happening every time before a nap or bed. She is also refusing her bottle alot. We Have been to doctor and ruled out any infections so what the hell has gone wrong. My husband and I are exhausted. As a side note, We are moving her from lactose free milk to lactose milk over the last 4 weeks (as per Doctor) but she has seemed fine up until now. Previous attempts at this failed as she would spew alot etc. Any help appreciated😭