What Causes A Lump Below The Vaginal Opening?

Hi. I have a little bump that directly bollow my vagina opening. It is flesh colored to my knowledge. When I dont have sex for longer than about a weeks period of time the 'bump' is flat, is not painful, I dont even know it is there but when I start having sex frequently this bump appears and it is slightly raised and it is painful. Not excrucianting pain but more like an irriating pain and it does not go away unless I stop having sex. I have been to my gynecologist about this and he said it does no look like genital warts. I have tried google and havnt come across anything similar. Any suggestions or ideas of what this may be?