What is the difference between a pimple o the lip and cold sore? How did I get it? I was not in contact with anyone who has it.

Depends. It kind of depends. The picture shows a classic cold sore. A pimple may be significantly different in its appearance, however, it is sometimes very difficult to tell. If fresh, within a day to three days, a culture can be taken or a dna probe checked. This can be definitive if positive, but not so if negative. Cold sores are exceptionally common affecting up to 75% of all americans.