That is absolutely not the hymen (which is an external piece of "skin"). It sounds like you may have a partially prolapsed cervix. I really would see a doctor, just to get the reassurance (if you want to avoid including your parents, would it be possible to arrange a phone appointment with your GP?). These things can get worse, so it's important to get it under control. This would not necessarily mean surgery, the most common sort of treatment for this kind of thing pelvic floor exercises if it's not too serious.