I've had a pimple on my upper lip or the mustache area for about a month now, why won't it go away?

Apparent lip pimple: This could be a "blind" pimple, an ingrown hair, a plugged sebaceous gland, or something else. After a month, it would be a good idea to have it looked at by a physician. It would seem by this time that it is unlikely to resolve on it's own.

See a doctor: Its been there long enough it should be looked at. Smaller pimples or cyst that don't clear up on their own can get larger, which is not helpful. Some growths that look like pimples are growths that need biopsed. Warm compresses and antibiotic ointment might give resolution in a few days, but if that doesn't work, time to get help.