Chronic headache what could be the cause?

Tension / migraine: First eye check . Next -Tension Headache most common reason ( not as in caused by tension but called due to feeling like.tension in the head) . Typically both sides affected. Simple analgesic should help. But If usually one sided, worse with activity, better with rest in dark room, associated with flashes of light or zigzaggy vision, irritated by sound and light then likely migraines. Seek help.