What Causes An Itchy And Painful Cyst On The Labia?

Have something like cyst on labia. At recent dermatology appointment, took biopsy, said non cancerous. Didn t seem to want to do further treatment. This has been for the most part like an open sore, the size of pencil eraser for over a year, once in awhile heals over. Said I could come back in and would prescribe steroid treatment. Since biopsy has retained it s original form, an open sore, hurts, itches, feels like an abscess. Plan on going back to Dr, but would like to be informed. The nurse I spoke with today said it was common and probably arose from a rash. Have never had a rash there. Any info would be appreciated.