Your problem seems to be nasal vestibulitis. And it is notorious for becoming chronic and also for recurring. But it is, in fact, easy to treat. Kindly consult your ENT Specialist
Is there any discharge from the nasal skin on top of the sore ? If yes, don't neglect it ; get it treated.
And don't be alarmed; it is not a grave condition.
But it needs to be treated because if this infection spreads it might be trouble you as it falls in the so called "dangerous zone" of the face; in this zone, infection spreads rapidly and becomes serious if neglected.