Headaches in the back of the head?

I have had a very bad headache in the back of my head for a few weeks, it feels like i hit the back of my head on something, but i have not, sometimes it hurts so bad i can't even move, and if i do i get really dizzy and can't see, and it is sensitive to light, i went to the doctors and he told me to try taking ZERC and if that did not work to try cold medicine, he even prescribed me a nasal spray , i have tried everything but he it has not worked, i have a hard time seeing sometimes, could it be my eyes? i have tried taking non-aspirin pain relievers because i am allergic to aspirin and ibuprofen, what could i take that would help, and what could be causing my headaches?