Dark spot on bridge of nose?

I'm 20 years old now, and since probably the beginning of high school (maybe a little earlier) I have had this recurring dark spot right above the bridge of my nose, right below the beginning of my forehead. It continuously appears and disappears, usually lasting no more than a few days. It is brown (I am half black and half white), it does not itch, and over the years it has no gotten any bigger or smaller. It is always the same shape: long and thin, vertical. Any ideas what it could be? Should I see a doctor?