Headache - pounding painful headaches at the back of head

I have excrutiating pounding headaches on both sides of the back of my head.  These headaches last for about 3 days and are almost debilitating.  It hurts when I turn my head, but especially when I bow my head to look down.  I feel my head pounding when I lye down and it hurts so much that I cannot sleep.  I have gone to several doctors, and they kepy prescribing pain medication - which does not help.  I had an MRI done, but it showed nothing.  I have been having these headaches 1-2 times every month for 5 years.  I cannot focus or concentrate, the only thing that temporarily relieves some of the pain are hot showers every couple hours and alternate hot and cold compresses on my head and neck until 2-3 days pass.  It is so bad I cannot drive and have had to take days off work.

Has anyone experienced this?  Please help!