It sounds like a Bartholin's cyst
. Bartholin's glands are two little glands on
either side of the opening of the vagina
. Sometimes they get plugged and swell up. They can also become infected. If this is what you have, the standard treatment is to lance the cyst, and put a ward cather in to create a little opening in the gland so that it doesn't heal shut and swell up again. This is a simple office procedure that is done under local anesthesia. Any gynecologist could do it for you.