I almost forgot to add: NO MORE SEX for you until you get this diagnosed! Not only for your sake, but your partner's as well. :-)
You probably have some kind of a vaginal infection. Since you have so much pain, it might even be bad enough to be classified as PID - Pelvic Inflammatory Disease. And because you are sexually active, you might even be dealing with a sexually transmitted disease. Take no chances and get yourself to a gynecologist. You don't want to let this go without treatment.