2.5 year old fighting bed time

2.5 year old used to sleep great. We would do bedtime routine and he’d put himself to sleep. The last 4-5 days he’s been fighting/ crying when we tell him it’s bed time and screams/cries on and off for hours. One night he fell asleep sitting and waiting in the crib, the other nights my husband has brought him into our bed to stop, so he doesn’t keep waking up our infant. Also, he’s been pushing back bed time routine.

Can anyone help explain this? Is there a sleep regression?

He is teething but we’ve never had this when we was getting the bottom molars. He’s been taking a 30-1:30 nap these days too.