I have something near my vagina and not sure what it is?

Okay so I have sex 3 times in the last two weeks and before that I hadn't had sex in a year. The first time I was a little sore but okay. the second was really rough and the third was okay. But i noticed it hurt when I would go pee. I saw like a sore or cut just below the outside of my vagina. And it's between my anus and my vangina but its closer to my vagina. And it has a red circle around it as if it's infected. Can anyone tell me what it could be? I am so scared that it could be a STD and I am only 18., Please help!