Could I have an overactive bladder (OAB)?

I'm afraid I might have something wrong with my bladder. I'm an 18-year-old female, and since I can remember I've had frequent urination and for the past few years it's gotten to the point that I don't want to go out with friends or risk going somewhere where there might not be a bathroom. I pretty much have to go every hour and a half or so, and I can hold it for a long time, but really only if I'm near a bathroom/relaxed at home. Some days, I have to go constantly and it's really uncomfortable; some days are just normal. I want to get on some kind of medication, but I wonder if I'd qualify. What should I do? What kind of doctor should I see?