Hi A., I am a mother of a 10 year old who had PDD NOS. Tony drove us absolutely crazy. We tried everything to get Tony to potty train and one day he just did it. Now since we have had a second son, Tony had taken to wearing pullups at night because he can't sleep all night without wetting the bed sometimes. I think you really need to make him sit on the potty once an hour until he goes. This is what we did with Tony. And I would tell him that because he can't tell you when he had to go, that you have to do this. PDD kids are sooo smart, I would bet he would start telling you. Then I would get with your school district and if he does not have an aide in class, have them give him one. He is entitled to one. Then he could tell the aide, or the aide can make sure that he goes at the appropriate time. Another thought might be that he is reacting to a dye in a food. Tony would react to red dyes and then have uncontrollable episodes.
You sound like you have your hands full. Best of luck, and keep in touch. And don't stress over it, I find when I stress over Tony, he feels it and then things just get worse.