It could be a batholin's gland cyst or abscess--i've had that, and it can be excruciatingly painful. You really shouldn't wait if you can help it--it isn't life threatening or anything, but if that's what it is, it will continue to get larger and more painful until it is drained. In the meantime, try aspirin or tylenol, hot, moist compresses, and if you can get your hands on some broad spectrum antibiotics, take them (but be sure to tell your doctor when you see him if you take meds). I'm only guessing here, based on my own experience, but if it's the batholin's, the Dr. Will make a small lancing incision (and you'll feel vast relief immediately). Depending upon the cultures and severity of infection, he might insert a medicated wick that will work its way out of the incision in a week or so, and prescribe antibiotics.