C.,
My DS (6) has food intolerances whose symptoms looked very similar to Autism and Sensory Processing Disorder.
I first noticed problems when he was 4 and started with my county (Ionia) and the children's services there. I called around and spent a few weeks chasing down leads and eventually he was tested by a woman who works for the county on a state grant. She suggested a couple of allergists to test him for food allergies / intolerances. It turns out he cannot have 7 different foods. Wheat, corn, soy, oats, milk, eggs, and yeast.
We have eliminated those 7 foods from his diet completely and have seen a huge change in his behavior. My son can now sit still (before he was bouncing off the walls), makes better eye contact, can tolerate touching (before I couldn't even hug him without causing pain), loud noises don't bother him as much (before he used to scream when the garbage disposal was turned on), he sleeps much better at night, and interacts better with peers and adults.
I'm not saying all of his problems disappeared. We still had to put him into a special education program (Early Childhood Development Delay) because his food intolerances caused him to be behind other kids his age socially. The preschool program was free and the teacher worked specifically on his social development issues in the class. Now our son is in kindergarten and is doing great. We are still working on sitting still and not interrupting and controlling impulses, but those are normal 6-year-old issues.
I don't know if my story is applicable to your situation, but I hope this helps. I found doctors not willing / able to help me, but the county was a great resource. All of the testing was free and once we knew what our son needed we started making changes. They weren't easy at first, but after a month or two we settled back into a normal routine.
Good luck. Let me know if you have any questions about food intolerances or allergists in the area. I would be happy to help.