Mri Angio 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? - mri angio

I had a constant headache all day, every day for 8 months. If I bend over it feels like someone has me with a stick on his forehead. Sometimes the headache becomes stronger, and then decreases. He had CT, MRI, CT angiography were negative. They have a lot of drugs, prescription and nonprescription tried without success. You still have no blurred vision. You have allergies, hay fever.