5 month sleep regression a thing?

5 month old has done every day nap as a contact nap for over 2 weeks. Will not do the crib at all unless overnight which we’re grateful for, but no amount of rocking or anything works.

For 3 weeks every nap has been a contact one and last night baby refused the crib outright. Husband and I did shift work overnight and are struggling today

What gives? We got lucky with our baby who had great and consistent sleep for the first 4 months. The last few weeks have been challenging

-are we in a 5 month regression?

-would some sort of sleep training mess up the overnight sleep?

-is baby not tired enough and we should work on 3 naps a day?