Help!!!! My son as been Inappropriately touching girls since the age of 7.

My son is 9 years of age and is displaying very inappropriate sexual behaviour.
From as far back as i can remember my son as never been a good sleeper at the age of 6 it was really bad and he use to get up at all hours of the night, go down stairs and turn on the TV.  I would catch him but other times i didn't hear him and remained asleep while he did this. At that point i feel he viewed something on TV that he shouldn't have done, something sexual. The first incident aged 7 happend at school he inappropriately touched a girl in his class on her private parts. The teacher did not know about any of this, my son told me when i went to pick him up. He seemed very upset then about what he had done and he did know he was going to be in trouble. I asked him why he had done it and he said he didn't know he just wanted to so he did. I calmly told him of the consequences of his behaviour and he was grounded for a week and he lost his privlidges. We also did a good touches and bad touches program at school and at home with him and it left everyone satisfied he wouldn't do anything like that again. At 8 i found him playing with his younger sister in her room and he admitted he had touched her on her private parts. I got my mother and his dad to talk to him. Again his reason was he wanted to do it so he did.  After that i do not permit him to play alone with any girl and he is always supervised when playing with girls.
Aged 8 1/2 he touched another girl in his class he was told off by his teacher, lost everything for a week again and lost his privlidges at school too. Three months after that he did it to 3 different girls in his class while he was under the table during a lesson he said he wanted to see what their faces looked like. At around this time he was diagnosed with Autism. I feel what ever i say or do doesn't have any affect.  My son as no friends at school or at home and because of this behaviour my son is isolated for fear of him doing it again.