In my vagina, my one lips gets swollen. what does that mean?

Bartholin Cyst: It may be Bartholin's cyst.Bartholin gland is normally not palpable but when there is blockage of the Bartholin's duct, it swells up and forms as a cyst.If it gets infected it can form ointo an abscess and is painful.But barthlin cysts do sometime get better by itself and other time it has to be drained.I will suggest you check get it checked by your gynecologist.