I have recently begaun seeing a girl who is about 5'7" but very thin. Also, her vagina is very tight combined with my fairly large dick, and from what we've experienced, shallow as well. The last few times we have had sex, it starts off fine, but after it gets harder and faster, she begins to bleed and often we have to stop because its painful for her, what is causing this? I've told her to see a doctor, but she says its fine. Have any of you guys or gals experienced this?