PTSD and Migraines are linked if you have either, you are more likely to develop the other unfortunately, we do not know why this is the case. The pathophysiology of both conditions are poorly understood and multifactorial in nature. Dr. Schuppe explains some of the research on the two and suggests possible implications in the treatment of trauma.
Here are links to two NCBI manuscript PDFs.
Traumatic Experiences, Stressful Events, and Alexithymia in Chronic Migraine with Medication Overuse. Bottiroli S. Et al
PTSD and Migraine: Epidemiology, Sex Differences, and Potential Mechanisms Peterlin, BL et al