Inappropriate Behavior

My son is 12 and has Autism (PDD). He has displayed innapropriate behavior to my sister and a friend. He asked my sister to zip his pants. He asked her some very personal questions. He is obsessed with hearing girls urinate. He has made phone calls to people asking them if he could hear them uninate. I have seen different conselors, and they have not helped. We do punish him when he does something like this. The problem goes away for awhile but it always comes back when he hears kids talking about sexual matters at school. Is there someone special somewhere that can help us. Do you have any advice for me?
PLEASE