Bump on shaft of penis? need help?

a girl and i dated for around 2 years. we broke up around end of 2009. when we broke up she told me she had contracted herpes and said i had given it to her. Last year (2010) i was tested and came back negative for everything but hsv 1 oral. A small bump was on my shaft for the past few days and i just though it was an inflamed ingrown hair or something. This morning i woke up and it is a bit larger, about 3/4 size of an pencil eraser and is a circle. It looks purple and is a bump, not flat. The tests that were negative were blood work tests and i have read that they can be negative but i could still have herpes. I need professional opinions or individuals with knowledge of the situation. thanks