Why do my gums bleed when I floss?

if your gums bleed its because: 1) your not flossing enough or 2) your not flossing correctley. everyone should floss at least twice a day (so whoever says floss once a day, is wrong...big time) and when flossing bring the floss all the way in until the floss stops (this may hurt the first or second time, but it is cleaning as far as it needs too, so bring in and make a "C" shape, like your polished a shoe. the more you floss the less it will bleed. see if you can get a professional cleaning then start doing that. as far as your teeth being loose, its hard to tell without an x-ray and perio probe (measureing your gum pockets) but ur only 17 so your teeth im sure are not loose, maybe they just feel like they are. hope this help:) happy flossing:)