Interesting that you are able to localize the bump on your lip to the time right after being involved in "a heavy make-out session." While not definitive, that does give some suggestion that this could be related to that event, although much more information and a physical examination would be required for correct diagnosis, which is why I recommend speaking with your doctor
. There are many viruses that are shared via the passing of body fluids. Herpes simplex virus is one of the more commonly transmitted infections, which can lead to cold sores and similar outbreaks in other regions as well. While this is one of the more common causes of symptoms that you are describing, there are many other possibilities as well. The best answer to know both how to diagnose and how to treat your symptoms is to speak with your doctor for a full evaluation. He or she will be able to ask further questions and will be able to provide a treatment if appropriate. In the meantime, please use appropriate hygiene to prevent from spreading this infection, if it is an infection, with others. Of course, things other than infection could also cause this, so please speak with your doctor.