I have a sharp pain in the center of the back of my head. What could it be?
You don't give us much information to go on, but it coud be ice pick headaches. For more information, see Ice Pick Headaches - The Basics.
That said, you need to see your doctor about this pain. It could be caused by any number of things, and unexplained head pain should always be checked by your doctor.
With no other symptoms, and a very sudden onset followed by a just-as-fast stop, the entire pain episode lasting from moments to brief minutes........if this sounds like you, look up "ice pick headache."
If not, you are going to have to tell us more info.