Just a cyst probably. I have 2 right now. I have gone to the doc, and they say, if it isn't giving you any pain, it isn't worth removing....Unless it is huge, and looks like you have a dick through your pants!.
Don't worry about it. I have had one of mine for about 5 years now, and it hasn't changed.
Have your gotten a pap yet? When you go...And its still there, just mention it to the doc..And they can check it out then.