It's common that when people suffer from head injuries, they also suffer from a neck injury since those parts are close together. There may be a certain point where you have healed from the head injury but still experience migraines due to the neck pain. Or it could be some combination of both. If you grind your teeth at night it can make the neck pain worse.

The best thing you can do is rest, drink water, eat healthy, and stretch your neck with yoga or physical therapy. Avoid coffee and other stimulants, even if they may be tempting because headaches are exhausting. I had horrible migraines for almost 2 years and it took me a long time to learn my triggers. Once I made some simple life adjustments, the headaches went away and life becomes way more manageable again. Good luck!