The “skin flap” that you describe sounds like it could be your labia, which are located on the outside of your vagina. You should have two labia, one on each side. The size of the labia can vary from girl to girl. Girls who have larger labia may complain of discomfort whenever they wear certain clothes such as bathing suits, and/or tights but the labia or “skin flap” shouldn’t hurt. It’s always a good idea to talk to your primary care provider about any concerns you have about your body.