E.K.
As with many of the responses, I agree with keeping him up later. He is probably changing his sleeping pattern. With my son I had to keep him up later and shorten his nap. A routine really helps. We do a bath and sing a song then brush his teeth then do the kissing goodnight round. Then leave him in there to put himself to sleep. If you are always putting him to sleep the both of you will deal with this going to bed issue for a long time.