Sleep help??

My 7 month old has been sleeping through the night and taking great naps during the day but all of a sudden a week or two ago he started taking AGES to fall asleep at night. He will fall asleep for naps just fine but as soon as it’s bedtime he just fights and fights and fights. Once he’s asleep he will sleep until morning but it takes him sometimes three hours to fall asleep 😔 with us going in every 10 minutes to comfort him or give him his binky. Is it just teething? Is he scared of the dark? What’s going on? What can we do to help him sleep?