Early in 2014 I had what I thought was a migraine on one side of my head for 3 months straight....every day, unremitting. My PCP referred me to a neurology clinic and they gave me an appointment with a certified headache specialist. She immediately suspected hemicrania continua and prescribed the medication which is used as a diagnostic confirmation. I had trigeminal nerve pain in my face from the beginning. Over the years the nerve pain has become more severe and more of the trigeminal nerve areas involved to the point it sometimes overshadows the headache pain. Based on symptoms described at subsequent visits she added chronic migraine to my diagnoses. My migraines feel much the same as HC but without the nerve pain.
Interestingly, although I had never given it much thought until now, there were times I would make an appointment with my PCP because I thought I had a sinus and/or middle ear infection and assumed my headaches where sinus related. All clear was the examination result each time. Of course that was before the headaches became continuous.