Dear T.,
Hang in there. This is a really rough time. We've been down a similar path and can finally see some progress.
You may already know that children with sensory processing issues very commonly have sleep difficulties and irregular circadian rhythms (and profound language abilities).
They also tend to take longer to regulate bodily functions and everything takes lots more time and patience. It's not in your head! This parenting is really challenging!!
And remember that your son probably is as frustrated in living in his body as you are having to parent him. A little empathy can go a long way.
There are several books (like we have time to read!) that offer practical tips in dealing with daily struggles and provide needed support and assurance to sleep-deprived frustrated parents:
The Sensory-Sensitive Child: Practical Solutions for Out-of-Bounds Behavior by Karen A. Smith and Karen R. Gouze
Raising a Sensory Smart Child: The Definitive Handbook for Helping Your Child with Sensory Integration Issues by Lindsey Biel and Nancy Peske
The Out-of-Sync Child: Recognizing and Coping with Sensory Processing Disorder, Revised Edition by Carol Stock Kranowitz and Lucy Jane Miller
The Explosive Child: A New Approach for Understanding and Parenting Easily Frustrated, Chronically Inflexible Children by Ross W. Greene
My best advice would be to find a caring, competent, skilled Occupational Therapist to help your son actually help to "re-wire" and feel better. Occupational Therapy is one of the key strategies to improving quality of life for everyone in this situation.
We had to search around the state (MI) to find this type of OT, but I highly recommend them. See more at http://www.thecenterforcd.com/
They've got all sorts of help under one roof (occupational therapy, nutrition, family therapists, ect.) and are accustomed to dealing with sleep issues and can make great referrals.
A good pediatric sleep specialist who understands the unique make-up of sensory-challenged kids could also be a great support to you. There are some tricks to regulating sleep with various light therapies, natural supplements, etc....
Many "experts" really don't have a decent background in this area so you might have to search for a while.
You can also check out referrals for help at http://www.spdfoundation.net/.
Hugs to you