When I tried to have sex with my girlfriend for the first time (it was the first time for both of us), and it would not go in. We tried different positions, but it kept sliding up, not even going into her. Anal worked pretty well, but she says that even when she masturbates she feels like she has a tight fit just getting one finger in there. Is there some sort of medical issue we should be worried about? How do we fix this problem of me not going in?