I Put My Fingers Behind Each Of My Ears, There

I put my fingers behind each of my ears, there is a big bone that sticks out behind my left one, but it isn't there on the right side. At times I got headache and I feel pain on the left side behind the ear. I have BP and diabetic problem also but big bone on the behind left ear is concern for me. Can it be tumor or something else.......pls guide