I have a pimple on my vagina lip for two weeks. it looks like a regular pimple. what could have cause it?

Sebaceous cyst: This most likely represents a blockage of the glands around the vagina. These can present just as you describe and often will drain on their own over time and with the aid of warm soaks. That being said, if it has persisted for 2 weeks, it is worth getting it checked by your OB to rule out other problems. It does not, however, sound like a typical std.