At your age I doubt it's anything more than a cyst. I've had them all my life. It's called Polycystic disease.
But when you can go see a doctor, go. Doesn't hurt to check it out.
Stop fretting and panicing. If it is something serious, which I doubt, you'll just deal with it THEN.
Don't borrow trouble from tomorrow, you have enough to deal with today.
Good advice for just about anyone.