I could be a couple of things, but it's best to get it checked out. I don't want to go into the range of things it could be, but one thing is, if your partner and you were both virgins before having sex, it's not uncommon for women to get ingrown hair down there that can become painful, swollen, and red. If you have a primary doctor, or a gynecologist, you can go to either to have an exam, and if they feel the need, they can take skin swabs or biopsies for testing. It's good that you are well aware of your body to notice this :)
Sara RN
i wouldn't worry to much about this. it sounds like a harmless cyst. i get them some times, try putting a hot cloth on it and the puss will usually come out, i know that sounds gross but it usually helps.