Lump found between vaginal area and anus, no skin irratation

I recently found a lump it felt internal and not apart of the skin, while washing myself in the shower, there was nothing on the skin, and it was off to the side between the vaginal area and the anus, it was about the size of a marble, and felt like it was attached to something. I have been in a monogomus relationship for over a year and a half, and during that time period have had two paps and been checked for STD's each time. Not sure what this might be, but when talking with a family member they thought some type of STD.