What Could Be The Dent At The Back Of Head?

Hi, i have a dent towards the middle back of my head. Where my ponytail. Its an extremely uncomfortable feeling and sometimes hurts to the point where i try to push it in. I feel as if i do get headaches from it and i was born with the dent according to my parents. What is it that i have and what can be done for this if that is possible? Also, is it necessary to do anything about it?