in addition to other suggestions, maybe try giving him something to do creatively.
Guitar, piano, band instrument, painting, drawing, writing a book (get an old typewriter if you dont want him on computer). Everyone has a creative element inside of them that can be nurtured. Expressing yourself creatively relax's you, makes you more intelligent, makes you feel accomplishment, all good things to nurture.
Is your environment healthy, stable, good?
Do you play 'lovely' music. Soft jazz, nice classical (not the kind that would get you overexcited). Is your home clean, organized, welcoming.
You'd be amazed how some people's homes are either overly structured and uncomfortable, or a pileheap of crap where only a rat would be comfortable.
Do you go to church? A nice church of evangelical Christians who can support you and your son. Pray infront of your son, outloud, pray for him, and with him. Teach him to talk to God.
Does this boy have a male role model in his life that he sees dailey or weekly. Get him a mentor if you can. GEt good men in his life that he can watch, see, imitate, talk too. Mama's boys lose in life, we smother our boys. Sorry fact.
Get ALL food additives out of his life, get him on healthy vitamins, ORGANIC fruits and vegtables. Teach him to garden his own foods, even if its just tomato plants and lettuce in the summer. Get all drinks but spring or well water out of his life. I don't even trust tea anymore. Teach him to grow his own sprouts. GEt a good juicer, teach him to juice.
Maybe he would like to do sports, yoga, defensive arts. Maybe he would like to film his own little movies, get him a video camera, but your going to have to let him process the films on computer.
Write everything down that you try. Keep a journal, dates, times, foods, diets.
To maintain a strick diet means YOU have to adhere to same diet, eat the same diet. It won't hurt you, it will help you. The food that is killing his brain can not be in the house. Because it is like a rat to cheese in a mousetrap, they will go for it, even if it kills them.
Brains are a delicate thing. He may never be ''normal'' he may never be able to live on his own. You have a damaged child. Mourn the man he will never be, accept the challenge of the human being you have been gifted with and keep trying. You can do this, you are strong, you are looking for solutions.
This is what I would do.