The term Migraine headache
you have used might be wrong in your case. It could be called us cervicogenic headache
. Since you have a old neck injury
you are prone for this.
Please watch out for your neck posture, do sit slouched? Do you have a rounded shoulders? I feel you might be having myofascial triggers which are causing the problems and this is bcos of imbalanced muscles. You could take a Xray and you must also do the RIGHT exercises.