I have had them before and they are painful and it is like a boil everyone is correct in this case its a cyst caused by an ingrown hair. I had two on each side before and I actually popped them myself and OUCH! Dont recommend it it was weird though when I popped it a very long hair came out of it like a cannon was totally gross! You do got to make sure if it gets too big to go have it lanced by a doctor also my niece had one of those and it got infected and got Mersa in it so I urge you to get it checked ASAP if it is as big as you say it is.
Yep I have had one of those before, it's a cyst. A pocket of fluid that accumulates, usually due to stress, not thoroughly rinsing the soap from the area and ingrown hairs, things of that nature. What you have to do is pop it, but I wouldn't really recommend doing it yourself, usually so much easier and smoother with a doctor's help. What I did though, cause I was too embarrassed to tell any one is I put a very hot hot wash cloths on it and held it there till it began to cool slightly. Then I squeezed the outside of it with one hand and pierced the center of it with the other hand. It burst out this really horrible greenish yellow creamy substance and was awful. But then I just kept antibiotic ointment and a band-aid on it at night and let it breath during the day and eventually it healed up and went away. Good luck!
Probably just an ingrown hair if u shave, or a pimple. Might want to get checked if sexually active?