What causes a constant headache encompassing entire head. Has lasted about 8 months?

What causes a constant headache encompassing entire head. Has lasted about 8 months?
I have had a constant headache, every day, all day, for about 8 months. If I lean over it feels like someone hit me with a club on the forehead. At times the headache becomes more severe and then tapers off. Have had CT, MRI, CT angio, all negative. Have tried numerous medications both prescription and OTC without any success. Do not have blurred vision. Do have hay fever type allergies.

There are losts of good answers, but the best answer:

Answer by ps@yahoo
What about getting your eues tested, could be bad eyesight causing this headache, its not normal to have a headache for as long as you have.Make an appointment with the optician lol.

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What to do if we have prolonged headache after hitting our head?

What to do if we have prolonged headache after hitting our head?
My friend hit her head on a tree forcefully. It swells on that area and she had a headache. After 2 days swelling is gone but she had headache. Since the day she hit she is having the headache. Now it’s more than a month and even now she had the headache. What should she do? Is it critical?
Will it be dangerous?

There are losts of good answers, but the best answer:

Answer by MP_doc
She ought to go to the doctor… it sounds like she may have suffered a concussion. It’s really best to get it checked out, as it can lead to other problems down the road if not treated.

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