It sounds like a bartholin cyst. It can go away on its own, but will return later. You should go to gyno and have them check it out. A bartholin cyst can become an abscess and your doctor will need to drain it.
it is problably just a pimple or white head is it sore to touch? just try and see if you can pop it that usually works. be careful and have safe sex always. sherri
It is possible it can be just a pimple. However, I would suggest keeping an eye on it. If it does not go away or if it increases in size, I suggest to go visit your doctor.