What Causes A Nodule On The Vaginal Mucosa?

I am a 25 year old female. History of excessively heavy menstruation and subsequently put on Orthotricyclen by my physicians/gynocologist in 2001 and have been on Orthotricyclen-Lo for about four years now. Two years ago, results of a routine pap returned as atypical cells of unknown significance. I had bi-annual paps for two years. I have been out of the states for vet school since January of 2010 and my annual paps occur when I can get home. I decided recently that I wanted to keep track myself (at least via palpation) to monitor any changes. Today, I felt a small, pea-sized nodule on the vaginal mucosa about 10cm's from the vulva. Could you help me with a couple differentials?