Possible std? Or maybe just a standard blister..?

A couple days ago I started to feel a little pinch on the outside of my labia majora. It started to hurt a little and even though it didn't itch, sort of scratching with just a fingernail seemed to help. It was not incredibly painful, just a little pinchy. I thought maybe an ingrown hair, but I haven't shaved recently...

Today when I urinated it stung. I decided to have a look. It instantly terrified me. It looks kind of like a peeling blister and my panties on it is uncomfortable.

I am sexually active, and have been with the same partner for over a year. Neither of us has ever had an std and neither of us has had any sudden symptoms. Until this sore. Of course I understand sores can be caused by many things, but I'm stressing out as I can't get an appointment until Friday.

Here is a pic.

//www.curezone.org/ig/i.asp?i=75240

I've cropped most of the private stuff out. I just need some advice, as everything I Google looks the same! Tweet