Migraines - Increasing In Frequency And Intensity

Any advice welcome. I gave a 12 yr old son who has suffered from occasional migraines for a couple of years. They are now increasing in frequency and intensity. GP has prescribed tablets to reduce symptoms and referred us to the hospital for further investigation. At the moment have no idea of cause/triggers but seem to occur in afternoons/evening. He just wants to go to a dark room and sleep mainly to avoid nausea. Would like to hear from other parents who have children in similar situation. Foods/stimulants to avoid?. Treatment that has worked? Possible questions to ask Consultant when we do eventually receive an appointment. No family history of migraines.