Hi, For this, there are few causes and most common is Bartholin s Cyst which is located midway of the labia, and protrudes into the vagina and may cause discomfort during sexual intercourse. Bartholin s cyst is formed when a Bartholin s gland is blocked, causing a fluid-filled cyst to develop. Bartholin s cyst is not an infection, although it can be caused by an infection, inflammation, or physical blockage (mucus or other impediments) to the Bartholin s ducts (tubes which lead from the glands to the vulva). Second, the infected hair follicle may form a small abscess, which can cause a small swelling, but it is associated with redness and throbbing pain. Proper diagnosis requires a proper physical examination of the swelling in question. You might consult a gynecologist who can examine and then decide on the appropriate treatment. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Ivan R. Rommstein, General Surgeon