Hi A.,
I agree with the comments you have gotten encouraging you to talk with his pediatrician about this.
You might also want to consider setting up a reward system for your son when he tells you he has pooped instead of putting his hands in his pants. He will need some specific, gentle direction on what to do; you could even role play with him, with you being the child and him being the mommy or daddy. Pretend to wake from your nap and say "My pull-up feels funny. I think I pooped. I am going to call mom/dad to tell her/him." This will model for him what you want to happen.
Set up a sticker chart with a reward for telling you he is poopy and maybe he gets a second sticker for keeping his hands out of his pants. If he does make a mess, have him help you clean it up. Clean him up first, having him put the poopy clothes in the washer after helping you rinse them. Then maybe a quick bath (no toys, ths is business) and then back to the sheets to clean up. Maybe he could help move the clean things out of the way. Don't be angry; let him know this is just a natural consequence. "When poop gets on the sheets/walls, we have to clean it up." Also tell him "Now we have less time to play because we need to clean up the bed. When you tell Mommy your diaper is poopy and keep your hands out, then clean up is easy and we have more time to play. I like to play with you." Be sure to reward him with play when he does tell you. Even do a happy dance when he tells you. Jump up and down praising him for telling you. Try to be there when he wakes up from his nap for a while to help him remember to tell you. Once he gets the hang of it, maybe put a picture of yourself near his bed to remind him to call you and tell him "When you see this picture, ths can remind you to tell Mommy when you pooped and to keep your hands clean." This positive approach may help him see the benefits of telling you he is poopy vs. putting his hands in his pants.
The most important thing is staying calm and not punishing him. Reinforce the behavior you want with praise and excitement. Take a deep breath. Cleaning up poop is not fun. With a positive approach you will soon be working as a team!Let me know what happens!