Darling, I feel you! I have not personally gone through this transition, but my children's godparents have. Their son had some developmental issues from about 18 months on. It took the doctors about two or three years to pinpoint Autism and celiacs disease. He has to be on a GFCF diet which means no gluten and no dairy.
It's an interesting thing, gluten. If the body does not process it right, it becomes like an opiate to the person. This can make him/her uncontrolable.
You might want to find a doctor who specializes in diagnosing and monitoring Autism. I know they say it cannot be diagnosed until kids are 48 months, but that little boy's sister was diagnosed at 18 months. She was displaying the same symptoms as her brother.
My best advice, read every label being wary of the "hidden" ingredients, be patient to learn what is acceptible and what is not, research the diet on the internet (there are a ton of resources, including recipies), email food brand companies to find out what would be acceptible for your son, and finally, try to find a support group, they can be extremely helpful in creative meal plans.
Google "gfcf", there are ton of websites. Oh, if you are near Regency Mall, there is a natural foods store in there with great gfcf foods, also try Native Sun, I think it is off 9A. I have a friend whose daughter is on a gfcf diet and she shops there all the time.
Keep your eyes open, you would be surprise what he can eat!
Anyway, best of luck to you and God bless!