What Causes A Pus Filled Bump On The Inner Labia?

yes i have a small bump like a pimple on the lip part of my vigina. it doesnt hurt. it did have some puss come out of it like it was a pimple. and just two days ago i went to my doc. to get an std test done. and i know he seen it but he didnt say anything about it and i forgot to ask him about it being there. and my test came back std free :) so is this normal? is it a pimple?