Unsure of what to do.

Hi, I'm struggling at the moment with my 14 year old son. He has asd, he is non verbal and over the last 6 weeks or so has steadily become more and more challenging, not only in his behaviours at home and at school, but also in his eating habits. He has lost nearly  a stone and a half in just under 6 weeks. He has always been a big boy. But he eats barely anything and now has stopped drinking really. I'm at my wits end, he woke up last night to purposely hit himself and I'm really struggling. If anyone can offer me any advice, I would be very grateful thanks so much.