Sleep regression?

I had a pretty decent night sleeper on my hands up until a few days ago. My almost 5 month old is now the most awful night sleeper. She sleeps from about 7:30 to midnight (if I'm lucky). She wakes up, I feed her, and then she is up for HOURS. It started with one hour, progressed to two hours and now last night she was up for 3 hours before she became so overtired she fell asleep. Did anyone else experience this or going through the same thing?!?! Any tips? When she wakes up I try and just ignore her (after I feed her)unless she starts getting really upset. We're currently co-sleeping (she's in a pack n play) Sleep deprivation is setting in...😩