Okay, fisrt things first: you can go to any clinnic or GYN without parental permission or notification. PLanned parenthood clinics usually offer a sliding scale, and you can get a local number for the closest one to you by calling, toll-free: 1-800-230-PLAN
In terms of the bleeding, I can't suggest any help ((nore certainly any medicine) without knowing the what and the why. is it possible your period is simply early? Is the bleeding like your usual flow? If it is, that is the most likely answer.
If it is NOT like your usual flow, extensive vaginal bleeding could really only be from vagnial trauma, miscarriage, hymenal tearing or vaginal abrasion, or as a possible symptoms of another infection or condtion. End story there, you need to see a gynecologist and you need to do as ASAP. There is no over-the-counter remedy to stop unspecified bleeding from any location on the body.
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