Sons migraines and head shakes

Hi my son of 11 yrs has always suffered with migraines. When he was 5, after his birthday party he sat on the stairs screaming holding his head and then fell asleep in my husbands arms whilst taking him to the car to hospital. The doctor couldn't wake him for 20 mins. He didn't seem concerned and said it was due to excitement and tiredness. Ever since he suffered loads of headaches and migraines ranging from 1 a week to 4 a week. Last year he developed a tic, shaking his head backwards and forwards and up and down. I asked for him to be allergy tested for his Migraines and the results came back as low risk to all the things they tested him for. He has quite a few days off school because of his Migraines and Im worried about the shaking of his head...could he have a trapped nerve that is making his head shake and causing him to have headaches.