I'm 19 years old and am quite concerned by a spot I have discovered on the outside of my vagina. I first noticed it a couple months ago and I thought it was just a skin tag or possibly where I may have nicked it whilst shaving so left it. Then a few weeks later in the shower I noticed it was quite painful and had swollen. I planned to go to the doctor but it had gone down by morning so again I left it. But today (13/01/13) it was slightly sore and when I looked, it has now turned black. I am sexually active but use protection and it is only the one spot.

Can anyone give some advice? Thankyou :)