You are seeing a 30-year-old male in a primary care setting who has presented with a headache. During a history, the patient informs you that his headache is on the right side of his head and that he also has a watery eye, nasal congestion and facial flushing. The patient also informs you that he experienced these headaches regularly at the same time every month but he does have pain free periods in between these attacks. What is the most likely diagnosis?