Weird cut/sore

I'm so sorry for the picture, but I'm worried sick. This showed up a few days ago and got worse because I messed with it trying to figure out what it was. It doesn't fit any of the descriptions of STD's and I have no other symptoms nor does it hurt. And it's not even like in my vulva area so I'm just confused. Has anyone else had this happen? Too much friction during sex or something maybe? It's about the size of a pencil eraser