I read about Pathological Demand Avoidance, after watching a programme about a group of children with autistic spectrum problems in a drama group. I must say, I cried my eyes out for the parents of these children. It often goes with autism, yet requires methods that are the polar opposite to deal with it. The prognosis is not good, as most will not be able to function in the world. I could see similarities in my son but however bad it was, it was not that bad! Difficult to see when he has spent an entire weekend hanging upside down from a chair rather than complete the writing the school has sent him home with (coz they do not want to deal with him!). It was useful background reading, as was ASD (see NAS website).
I have found daily routine good. He did not learn to stay up late on the computer until after A levels, and always got a good sleep and good meals (he probably eats a very good healthy diet, much better than his contemporaries, after such a difficult start).
I remember having a family star chart when he was about 9 (we went through a stage where the whole lot of them were misbehaving) and he just was not bothered at all. Later, we tried drawing up 'behavour contracts' and that didn't work either. As he got older we used to talk about what he wanted to do, how he wanted to get there, and how spending all day shooting pixelated men would not achieve it, and that it was under his control to do something about it. Whilst none of this seemed to help at the time, I think it may have had some effect in the long run.
If you can try and relax and appreciate him when things are going well, it will help a great deal. It is not easy when you feel like you are being put through the mill. One of my son's teachers pointed out his sense of humour, which had completely passed me by! Felt a right idiot! (Brilliant teacher, by the way).
Do get some help if you can, but don't count on it. Look after yourself, and stay strong x