Teenager Autisim challenging behaviour

Hi I am new on this. Really could do with someone to share similar experiences with me. My son was diagnosed at 3yrs, he is now 11. He is a big lad bigger than me as I'm petit. I am a single mum so there's no second hands to help  

When he has his trantums, they turn into horrible meltdowns that nothing I can do will help him to calm down. My struggle is I can't physically control him, he will hit and kick me, ly on the floor and kick legs high up. Obviously more hard in the community. Just wanted to ask if anyone has a child similar age with similar outbursts and what do you do in this situation. 

Thank you