I've had this lump on the the back of my head since I was in my teens. It never bothered me but sometimes it keeps me up at night wondering what it is. It would be nice to know what it is, or if it could be removed?

Lumps. Without actually examining the area, it is difficult to know what this lump may be. As you've had it several years and hasn't bothered you the odds are it's nothing to worry about, but if it is causing you anxiety because you don't know, then have your doctor take a look at it. Put your mind at ease.