First guess: Hormones. Everyone reacts to adolescence differently. Acne, moodiness, etcetera. Some get really, really turned on.
Also, just out of sheer curiosity, is this by any chance right around your monthy days? It's not unheard of for that to affect your urge to masturbate. Just sayin'.
Anyway, persistent arousal syndrome is something that isn't too subtle, I think. While - I guess would be the best word - while active, the simple act of, say, putting your underwear on would be enough to make you want to masturbate to orgasm.
I guess an easy way to find out would be to have a good little orgasm, and if you get strong urges within an hour or two... then there's a chance you have it. In the meantime, just do something that would keep your mind off the issue, like a movie or something.
Persistent arousal syndrome is still new, and hard to diagnose for sure. If you seriously suspect you have it, I urge you to seek attention to find out for sure, as it could potentially make daily life difficult for you later on.