E.C.
We just went through something similar with our 2.5 year old. He wouldn't go to sleep at night (sometimes). We finally figured out that it was his naps. He had been outgrowing his naps (sometimes taking an afternoon nap, sometimes not, even when we laid him down) for a while. He was sleeping at night when he didn't take a nap, and staying up to the point of exhaustion when he did take a nap. We quit laying him down for a nap, and now he goes right to sleep every night. Sometimes he falls asleep at his old nap time, right where he is playing, and then I just let him sleep for an hour or so, there where he fell asleep (I know that sounds bad, but he's a light sleeper and would wake up and not be able to go back to sleep if I tried to move him). It seems to be working. Maybe your son is too old for a regular nap, too. Hope this helps!