Does he sleep a lot during the day if he is then that will disturb his nightime sleep, if he still needs or wants to sleep in the daytime let him sleep for a while but not for hours, if he is in Day care they do get a long nap so check that out. What time does he go to bed ,is he having enough stimulation during the day, fun and games outside activities, Dont give him food or milk before bed as this can get him going, make his evening meal the last one,maybe a sippy cup of water an hour before bed. Then put him into his crib/bed and leave him if he yells thats okay the more you go in to him the longer it will last,So,, make sure he has played, make sure he is tired , the let him get himself to sleep.Good Luck you are not along with this it is a very common issue..