For at least a year and a half, maybe longer, I have had a pea-sized lump on my scalp on the back (right side) of my head, near the top. It doesn't hurt or itch, and it is the same color as my scalp. It does not poke through the hair; in fact, you can only feel it if you move all the hair around it and rub your finger over it. But right where it is, I have a bald spot. I had always thought it was some kind of scar, but I'm a little worried. What could it be?