I would guess a Bartholin's cyst, since it's not red or *****. It is extremely unlikely to be cancer, given your age. But BluCrystal is right, you'll have to see an ob/gyn or your GP to find out for sure. You can soak it in a warm bath or with a warm washcloth, which might help it drain (and at worst will do nothing).
The only sure way to find out what it is is to see a gyn about it. Make an appt so you can get treated and not have to worry about it anymore. Blessings - Blu