eating issues

I have a a 12 year old son who has autism and has been diagnosed since he was 6.

He has always been fussy with his food, but just recently we caught him making himself sick on an number of occasions and we know of other times he has been sick many other occasion but we dont know if he has done that himself. He is also very underweight and all his bones are visible through his skin.

We had him back to camhs where we have been told it too early to diagnose anorexia . Also they said to give him vegetable fats in abundance such as nuts seeds and fish !! not gonna happen !

Just after some advice really or similar experiences

Thanks claire x