Its probably a boil. Which can be caused through shaving, they normally happen because of infected nicks or ingrowing hair. Apply hot flannels to it and that will help its lifecycle pass quicker, once tyou have had one though they are prone to returning again and again. If you do find you get a problem with it your doc can prescribe you a special bodywash that kills the bacteria that causes them.
Could be a Bartholin's cyst - It's impossible to be exact so you need be seen by either a GP or Genitourinary medicine clinic or gynaecologist if you have direct access to one.