Advise please

im a mum of an 8 yr old boy, he has autism classed as high functioning autism and is in mainstream school. My hardest battle is with myself I’m not sure how to discipline as it always seems to descend into chaos with him throwing things hitting me or anything around speaking back and saying things like I don’t care, I won’t do as I’m told, you can’t make me.  It can all start from something as little as it’s dinner time come and sit at the table please? I’m really struggling to work out is he just being a badly behaved child and my discipline is not right or is this autism related? 

Recently im also having issues with him at school with teachers stating he’s refusing to do his work and we have always had issues with his eating at school and now they are starting to say he can’t concentrate in the afternoons because he hasn’t eaten anything at lunch. 

I cant seem to find any support. The pedestrian only sees him once every 6mths and isn’t that much help, last time she told me not to let it get to the point where he loses it but I can’t see how I can let him run around doing as he likes when I have other children in the house.

 Any advise would be appreciated