Hanging Columella on Just One Nostril, What Can Cause This?

The skin of the columella takes on the contour of the cartilage underneath it.  Your bump can be due to either the alar cartilages or the bottom end of the nasal septum.  A detailed exam would help decide this and the correct cousre of action to correct it.

Asymmetry of the columella is most likely due to asymmetry in the cartilages running down from your nasal tip to the lip. it could also be due to a deviation of the end (caudal) septum. You really need an examination before anyone can tell you more.