What Causes Skull Indentation?

hi. i have noticed this week i have a dent in my skull just by the hair line going towards the middle of my head, actual there is 2 in the same place about 2cm apart, i do suffer from migraines espeacialy round the time of the month and they can be very painful like am being stabed in the eye but its only ever one eye. these dents were'nt there a few weeks ago.