Hello, Thank you for your question. Vagina Sac (cyst) can be refer to Bartholin cyst. A Bartholin gland cyst is a small sac of fluid sac of fluid that forms when the opening of a Bartholin gland is blocked. All women and girls have 2 Bartholin glands just below the opening of the vagina. The Bartholin glands make small amounts of fluid. The fluid helps keep the vulva moist. (The vulva is the area around the opening of the vagina that includes the labia.) If something blocks the opening of a Bartholin gland, fluid can build up and form a cyst. This usually happens in jsut one gland, not both at once. Most women notice a lump in the vulva, but Bartholin gland cysts often do not cause any other symptoms. If they do, the main symptoms are pain or discomfort when a woman walks, sits, or has sex. If a Bartholin gland cyst gets infected, it can form an abscess. An abscess is a pocket of pus that can cause a lump to form on the vulva. Symptoms can be severe pain, swelling, redness. You should see your doctor if you see or feel a lump in the vulva inn vagina, it is painful to walk, with or have sex. Your doctor may be can see what is the real mass in your vagina. If you have an abscess your doctor will send a sample of the pus to a lab for testing. This can show what type of germ caused the infection. The treatment depends on your age and whether the cyst is causing symptoms. If you do not have symptoms, you might not need any treatment. Otherwise, treatments can include: draining the cyst or abscess and antibiotic are usually not nedded. But you might get them in some cases, like if you have had an abscess before or are at high risk of the infection spreading. Surgery maybe need if the draining fluid and putting in a balloon does not work well. Hope I have answered your query. Let me know if I can assist you further. Best regards, Dr. Heang Chan Raksmey, General and Family Physician.