Hmmm, good question! If it's been hanging around so long, and it's not painful, it's probably not a cold sore. It might be a case of a clogged pore or pimple (see acne), or an ingrown hair. (This is more likely if it's on the skin surrounding your mouth, rather than on one of your lips.) If it sticks around and is bothering you, get it checked out by a dermatologist.