Could be a cold sore. "cold sores" are usually caused by the herpes simplex type 1 virus. They respond to antiviral medications. If it's not healing, then an office visit may be worthwhile. More concerning, though, is that a basal cell skin cancer can have a similar appearance, particularly if the lesion is not healing and doesn't respond to treatment after some time.
Mega-balm. Use lip balm with sunscreen, petrolatum/beeswax. Reapply often. Cover your lips with even more lip balm, then a scarf if you're going out into the cold, dry winter weather. Don't lick your lips [spit=bad]. Drink lots of water.