3 months - fussy not sleeping

My LO is 3.5 months and typically is pretty happy.

The past week she has had TERRIBLE sleep. Like half hour to 2 hour stretches, 3 at the the very most for the first one... only if we are lucky.

Today, she would eat, be happy for like a half hour, and then scream and cry until we could finally get her to sleep, which sometimes took a half hour. This is so completely out of the norm for her.

Any insights? I’ve read about the 4 month sleep regression starting early or just a growth spurt, but I just don’t know. We are STRUGGLING over here! Help!