it's not something you always have as part of it is a hormonal imbalance, although it's hard to say whether the hormones going out of whack cause the symptoms, or whether something else causes the hormones to go out of whack.
It's quite a specific procedure to diagnose, so they're unlikely to pick it up unless you or they are specifically looking for it. The two tests I had, which I understand are standard, are a blood test for hormone levels (in particular, too much testosterone) and an ultrasound scan of the ovaries, where they look for additional cysts.
Skipping 3 periods is definitely not normal IMO and worth getting checked out. Doesn't mean you have PCOS but it should be one of the things your GP and you consider.
Once you have it, there is no official 'cure' and most of the treatments involve managing the symptoms that bother you, which vary with each woman.
If you do turn out to have it, I'd recommend books by Colette Harris, but I really wouldn't read them until and unless you know you have it, you have symptoms that bother you and you want to do something about them - they contain a LOT of information and there's no point trying to absorb it all if in fact you have something else.
Very best wishes - it's far from the worst thing you can have, but it can take some getting used to if that's what it is.