I would assume there is something routine that is happening for the headaches to only be happening at night time. Is there something that you do, eat, drink etc that is routine enough and matches the pattern of headaches? What about stresses the evening brings, having to cook, clean, answer the phone? Might be worth taking mental note of what is happening on the nights you are having the headaches to see if there is a pattern......

just my two panadols worth....lol