What Causes Swelling, Pain And Redness In Vagina?

Hi, the other day I noticed some soreness on the left side of my vagina, in between my labia Majora and my labia minora. It felt like a small lump. I had a shower cleaned the area and put a tiny bit of polysporn on it. It was as ok the next day then that night I noticed it again but went to bed. In the morning it was worse... so I got a mirror and had a good look. It looked a bit tender with some redness but then I noticed this swollen line about a inch long that almost looks like a vein. That is the tender, swollen area. I have not have any intercourse in a while so I know its not sexual trama or anything. There are no blisters or bleeding, just some swelling and pain. Any ideas?