RBM, try not to fret. when I was a teenager, I wouldn't get it for months, would get it twice in a month, one month it'd last for 8-10 days, another only one or two, etc, etc. I'm not saying it wasn't fun, but I didn't even begin to approach any sort of regularity until I hit my twenties.
I think there's some truth to the notion of your hormones stabilizing out and establishing regular patterns in adolescence, and that you can expect more normalcy in young adulthood.
What I *would* be concerned about is extraordinarily heavy bleeding, very long periods, bad pain, fatigue, etc. If any of this happens, I'd head to the doctor, have a blood test done (might become deficient), and see what can be done to help you get back on track as your body learns what to do as a woman.
*hug*