A 9 year old boy presents with a unilateral headache which o…

A 9 year old boy presents with a unilateral headache which occurs twice a week for the past 6 months. It is not associated with visual or auditory symptoms. The headache lasts about 2 hours and sometimes it is associated with nausea and vomiting. It is relieved by sleep or by painkillers. His systemic examination is normal. What is the most likely diagnosis?