Hi, and thanks for your medical question on eHealth forum!
What you have is probably a Bartholin cyst. On each side of the vaginal opening there are Bartholin's glands which secrete fluid to lubricate the vagina. At times their openings become obstructed causing fluid to accumulate in the gland, resulting in relatively painless swelling called a Bartholin cyst.
You can soak in a tub filled with a few inches of warm water (sitz bath) several times a day for three or four days. This may rupture cyst and which will then drain on its own. If this does not help, then please consult your gynecologist for incision and drainage.
Also please consult your gynecologist to rule out Herpes and boil. You must get your blood sugar checked for diabetes. Hope this helps. Take care!