Bedtime issues!

Me

Usually I put my son to sleep right before I leave for work and my mom stays with him during the night. However the last couple nights I've been off (thanks convid 🙄) and my baby hasn't been hardly sleeping! Last night he didn't go to bed until 11:30pm and tonight it was midnight!! We're not doing anything differently so I don't understand. He is teething pretty bad right now but this is horrible! Any tips or thoughts as to why he won't sleep?