What Causes Painful Sore In Vagina?

My vagina area hurst and is kinda sore. There may be like a sore or an ulcer there. It has been gradually getting worse over the past week. I am 18 now and I had this same problem before when I was 16. I have never had sex, or anything close to it, so I know that this is not a sexually transmitted disease. Is there anything that I can do on my own to get rid of this pain? or do I have to go see a doctor?