You should see a doctor. It can be anything from a boil to a genital wart. I don't think its dangerous. Bottom line, no one can tell you what it is. If it's abnormal for you, it needs to be examined.
stuff like this i SO ddifficult to even suggest via the internet. especially sine you describe very little about it. like has it grown in sixe since? what color is it? whats the texture? that sort of stuff. over the summer, i saw a "lump" down there and i agonized about it for weeks. even posted here. i thought i had all sorts of things. in the end, its part of the area (trying to be tactful)its called "rugae" (sp). its kind of like a corregated texture. if i squatted down w. a mirror, it kind of "bulged" out more. i was scared but monkeyflower (here on MH) suggested that and i went to the dr. and she said the same thing. is it possible thats what you are seeing?
could it be a rectocele or cystocele? could it be a bartholins cyst? check them out online and see.