3 Answers

Per the Mayo Clinic:

Although much about the cause of migraines isn't understood, genetics and environmental factors seem to both play a role.

Migraines may be caused by changes in the brainstem and its interactions with the trigeminal nerve, a major pain pathway. Imbalances in brain chemicals, including serotonin — which helps regulate pain in your nervous system — also may be involved.

Serotonin levels drop during migraine attacks. This may trigger your trigeminal system to release substances called neuropeptides, which travel to your brain's outer covering (meninges). The result is headache pain.

Migraine headache triggers
Whatever the exact mechanism of the headaches, a number of things may trigger them. Common migraine triggers include:

Hormonal changes in women. Fluctuations in estrogen seem to trigger headaches in many women with known migraines. Women with a history of migraines often report headaches immediately before or during their periods, when they have a major drop in estrogen. Others have an increased tendency to develop migraines during pregnancy or menopause. Hormonal medications — such as oral contraceptives and hormone replacement therapy — also may worsen migraines, though some women find it's beneficial to take them.
Foods. Some migraines appear to be triggered by certain foods. Common offenders include alcohol, especially beer and red wine; aged cheeses; chocolate; aspartame; overuse of caffeine; monosodium glutamate — a key ingredient in some Asian foods; salty foods; and processed foods. Skipping meals or fasting also can trigger migraine attacks.
Stress. Stress at work or home can instigate migraines.
Sensory stimuli. Bright lights and sun glare can induce migraines, as can loud sounds. Unusual smells — including pleasant scents, such as perfume, and unpleasant odors, such as paint thinner and secondhand smoke — can also trigger migraines.
Changes in wake-sleep pattern. Either missing sleep or getting too much sleep may serve as a trigger for migraines in some individuals, as can jet lag.
Physical factors. Intense physical exertion, including sexual activity, may provoke migraines.
Changes in the environment. A change of weather or barometric pressure can prompt a migraine.
Medications. Certain medications can aggravate migraines, especially oral contraceptives and vasodilators, such as nitroglycerin.

I have seen some people use flax seed oil for support. For some it relieved symptoms. An alternative new therapy is called frequency specific micro-current. I know some women who have tried it and felt better.

the cause is......dialted blood vessels in the head. I used to get a migraine about once a month......just before my period. sometime  it would last for as much as 3 days. Sometimes, not having enough sleep and then a lot of stress at work would cause it.  After I went thru menopause, I never had a migraine again. So, it's got something to do with hormones, too.