Almost only seen right inside the front of a nostril, a Furuncle is an infection, usually by the bacteria Staphylococcus aureus (“Staph”). They tend to occur at the entry to the nose, due to germ overgrowth during/after a cold, or sometimes from nose-picking. Treatment is with antibiotics that work against Staph.
The Herpes simplex Virus can occur anywhere on the head-and-neck (Herpes simplex Type-1); Herpes simplex Type-2 can arise anywhere genital secretions happened to wind up; both are rare in the nose, though not impossible. Immunocompromised patients can have a variety of infections.
All these are uncommon. The main symptom may be nasal discomfort rather than congestion. We can usually see such sores if we look carefully into the front of a nostril as best we can.