K.J.
My now 5 year old son went through the same thing and more often when things changed around the house. Like a routine, a familiar item in the room taken down, etc. The list is endless. Teething is still a possibility. Eventhough you don't see or feel them, he maybe cutting them. But also, on a completely different note...If he is in the beginning stages of walking, his legs may be sore. He is trying something new with his body and that could easily affect sleep.