If it does not improve, see a gynecologist.
If the head of the bump is white, and painless until you screw with it, and feels like a solid hard pimple that wont come out, its probably a cyst from a clogged pore or hair follicle. Ive had these, they will get infected and swell up if you mash on it. These have to be cut out normally. Put neosporin on it and don't mash it, the inflammation will go down and see your doctor for removal. I have tried many times to mash them out, it always comes back, even though it seems to go away for a while.
If it is a sore, and it hurts, it could be herpes II. It could also be a vaginal wart caused by an STD. More than likely though it is the first scenario, or you would have mentioned pain.