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You have not mentioned whether you are using spectacles or not. Since you are having this headache for more than 3 years, first thing you need to do is test your eye sight and if corrective glasses are required, use it right away. If it is not eyesight which is the cause, then you need to check whether you have any ear or dental problem, which can also cause headache. Another cause is frontal sinusitis
. Then there are many other causes which could lead to chronic headache and to find these causes you need to have a very detailed investigation. Best would be to consult your family physician, and he should be able to direct you to the right specialist for further investigation.