Pathological demand avoidance

This is going to be quite a long post.
Contact the NAS for advice. They can answer your questions and provide information. Is he at school or not? If not ask the GP to refer you to a autism specialist for further assessment and diagnosis. Make a list of what you have been noticing in your child. Do you have a social worker or not? 
Make sure your questions are answered. Inquire about support groups for parents. Get their details then contact them for support and help. Phone up your local council to make a formal assessment request. Or email. 
Use the directory found at https://www.autism.org.uk/directory.aspx to find appropriate services for your child as well. Take care of yourself as well. Do you have other children or not? Look into respite care. Again your council can help you with that. Look on the website. Join a online forum for support or guidance.
Spend time alone. Go for walks alone. Use any opportunity offered to take care of yourself. Nap, shower etc. Get relatives to support you. Talk to other families affected by autism. 
Also see about direct payments. You can use them to help build his confidence up in social situations like parties etc. Check out this useful info sheet on friendships -https://www.ambitiousaboutautism.org.uk/understanding-autism/independence/making-friends
Get a carer assessment pronto. Have you applied for DLA yet? You can use the money in ways that benefit him. We also applied and were awarded but my son does not have autism so how we use it is different. I hope you get the support needed.
Use the money to pay for his therapy and social skill classes. You could also spend the money on things like a pair of noise cancelling headphones etc. I recommend getting help to complete the application form.