Headache that goes away with exercise

I have a constant daily headache that is only fully releaved by exerting myself or when my heart rate is elevated.

What could be causing this? I have been to three doctors and had multiple tests including blood and CT scans.

Does anynoe have ANY information? Please do NOT post "You need to see a doctor" I know this and I have tried but they can't find anything wrong!

What could they be missing?

I am begging for some advice before I go crazy!!!

[ed34]

just as a matter of interest, what is your blood pressure. Do you take nitrates?
how long have you been getting these headaches? there are so many possibilities
for headaches that you could write a small book.

[ed34]

Another question, where does the pain seem to be eminating from? Sometimes headaches feel as though they are coming from the neck, sometimes the top of the head, sometimes behind the eyes.

[chaseap01]

I have been having them for about 2 months now. It seems to hurt on my lower forhead or behind my eyes.