There is a small hard bump on my scalp. It rarely pains. I noticed this bump atleast 6-7 years before. It varies in size slightly sometimes it is slightly bigger than the usual than after some time or a day it get back to its original size. Normally whenever there is a headache I feel it as slightly bigger than the usual and when I feel relief in headache its size get back to normal not always but I have noticed this a few times. I want to know the cause and whether it is some underlying disease.