Please help I am desperate

Hi I haven't been on for a while as life was jogging along nicely, but something has come up that I am totally out of my depth, and comfort zone with, and I am hoping some one here will be able to help.

My son is almost 13 now and has Aspergers.  He is a wonderful articulate loving boy, who has been through a really rough time, that we are coming out the other side of.  He takes prozac to manage his anxiety.

He is going through puberty and has announced that he is gay, that is fine and not the problem, (I don't care if he loves a blue koala as long as he is happy), I mention it because it might be related to his problem.

He has for a while had wetting and soiling issues which have had me stumped, because he used to be really reliable.  Tonight after a lot of reassurance he sent me this message over skype as it was easier than talking to me face to face (I get that it is embarrassing for him at his age>)

the reason why I am urinating is cus I am a idiot and I stick my hand up my but witch cause me to wee. and I want to stop cus its not helping and idk what to do I am sorry

 but I cant stop and I don't know hy

 why*

I understand that it is a pleasuring thing and also probably sensory aswell but I have no idea how to talk to him, to help him stop.  It is having a huge impact on his life. he is needing lots of changes of clothes, his hands and nails and around the nails are always filthy because of where they are going, and his is having repeated bouts of diarrhoea.

Sorry to ask for help but I am totally utterly stumped, and I want to help him, especially with school coming up