Have you written it down? Does he normally go down for a nap like 2 hours later? Start by waking him up at the same time every day. And then maybe putting him down 2 hours later (this is what my daughter did at that age). Have a set bedtime routine. If he's hungry though feed him. If he's tired and not just sleepy let him sleep. It takes time to get him on a schedule.
Well what I did is... I put my son to bed at the same time every night and also the same time for his naps throughout the day even if he wasn't tired and when he cried I let him do so for about ten minutes or so then I would go in calm him down and then put him back down and he would fall asleep eventually. I did this for about a week and now he has his own sleep schedule on enap at noon one at 5:30 and bed time is at 9:30 and he wakes up at around 6-6:30 in the morning. So try this and let me know how it helps you out.