I was thinking the same - while we can help here, I do think you need to get some highly specific advice directly relevant to PWS.
A classmate of difficult child 3's (former classmate, at the moment) is PWS and about 12. Currently in placement because his mother (who I think has been absolutely brilliant, a saint and eternally vigilant) finally couldn't cope because his problems escalated to such an extreme level to the point of doing harm to himself as a result of his obsession with eating ANYTHING plus his mother's (necessary) tight controls. It's not satisfactory for this boy at the moment, they are sedating him in order to cope. We saw him at a dinner (ironically enough) and I was horrified to see how bombed out he was; his mother wasn't happy with it either. But she was a bundle of nerves from the long-term stress she's been through.
He's my only personal experience with PWS; yes, there are other behavioural issues loosely connected to the PWS which, being more general, could be worked on here. But you might find that what your son is doing, while not technically psychiatric, might still be more familiar to someone specialising in PWS.
But hey, grab whatever help you can find, wherever you find it. Pick our brains by all means. A book we swear by is "The Explosive Child" by Ross Greene. There are other really good books, people here will share their experiences. I know he's no longer a child but I find that book helps with a wider range of interactions than perhaps was originally expected. If you go over to Parent Emeritus you might find some good information over there, too.
I suggest you keep a diary (if you haven't already been doing so) because it could help you find a pattern to his behaviour. A diary can sometimes help you see this sooner than you would otherwise. I used to count on the doctor to keep a good enough record - they don't.
Anyhow, welcome.
Marg