C.P.
Why don't you ask him?
He's not a baby anymore. He has thoughts and ideas and fears. Talk to him. Tell him that you see that he's having a hard time behaving lately, and since you're his mom and it's your job to make sure he grows up to be a good, kind, honest man, you'd like to know what you can do to help.
We're so quick to sweep our kids off to the pediatrician like a pet to the vet, especially when they're little and they can't say what's wrong. But he's big enough to talk to you now...see if you can glean something from his bright little brain.
When he talks to you, be open minded. Consider his feelings and his level of critical thinking ability. See if you can work together to figure out a plan. I'll bet the farm that he doesn't like his behavior any more than you do, he just doesn't know what he should do.
Good luck! And let us know how it goes!