Help speaking to 11 year old about Autism

My son was diagnosed with ASD early last year.  He is 11 yrs old and transitioned to mainstream secondary school last September.

We are having issues at school and are working hard with the school to assist my son to help him to manage.

My son has never really listened to what Autism is, or how it affects him.  I have tried talking to him, so has his paediatrician.  I have tried showing him books, You Tube videos, but he refuses to listen.  Yet he will often get very upset with himself because of his 'head' being busy; not being able to make a decision; feeling different in school and amongst his peers.  The more anxious he is getting about school life, the more new tics and OCD behaviours are appearing, it is a vicious circle.

I am desperate for an 'autism professional' to speak to him to explain what Autism is and how it might be affecting him. He might then start to understand himself better and his behaviours and feelings. But I can't seem to find any such professional to help. His school and the Advisory Teaching Service don't seem to be able to help.

Does such a person exist?!  Someone who understands what Autism is like - perhaps an Autistic person themselves - who can talk to a pre-teen to help discuss their diagnosis and how it feels?

I feel like we pushed on for four years to get a diagnosis and then when it comes, the door is shut.  Finished.  We are not finished, this is just the beginning. My son seems so alone and confused and I just don't know who to turn to for help.