Hello and thanks for writing. I can understand your concern and would try to help you in the best possible way. Get his Blood Pressure checked, as rarely hypertension may even be a cause in children. Other causes at his age could be migraine, head injury, vision problems, less than normal sleep or stress or any other cause. I suggest you consult a doctor and get him worked up for these conditions. It would need a complete medical history of his problems, physical examination and a few relevant investigations. In the mean while try to keep him hydrated as you already are, and avoid TV and Video games that put undue stress on eyes and mind and engage him in physical activity as much as possible.