There could be many reasons for a headache... from the most banal (fatugue) to the most serious (brain tumor). Sometimes the reason is unknown, like migraines. First, go to your doctor to measure your blood pressure and to request standard blood analyses. Then, you can visit an ophthalmologist to examine your eyes for any refractor anomaly or glaucoma (increased eye pressure). You will also need an ENT-specialist to examine your ears and sinuses for inflammation.