Overactive bladder medication?

I need non-over the counter medication to help relieve my over active bladder..im 15 and in high school and i have to go to the bathroom before every cl and during cl a few times a day..so i go about 7-8 times a day during school because i just get this unbelievable urge to urinate. I talked to my mom and dad about this but they dont listen at all, even if im crying to them they just ignore me. I said I want to see a doctor but they said that I dont need to..so is there any non-over the counter medication i can go out and buy that will stop this ridiculous urge to urinate? This is ruining my life, and tomorrow I have PSAT which means i cant go to the bathroom for 3 hours and im just soo scared that i dont even know if i want to go to school...PLEASE someone help me, i was searching google but i found nothing...