PDA (pathological demand avoidance)

Hi, 

My son is 12 years old and has asd and pda, I'm really struggling with his pda, I know how to speak to him to avoiding making demands but he still refuses to do anything at all, brushing teeth, going to school, getting out of his taxi at school, washing, going to sleep. 

I'm literally exhausted and I don't know how to manage it.. 

My son's school are ringing around for support but I'm not hopeful as we haven't received any tidy support since his diagnoses almost a year ago.. 

Any advice would be much appreciated. 

Thanks!