Sorry to reply so late to the comments about sweeteners, but I think that my migraines are caused by drinking stevia-sweetened coffee on an empty stomach.

I recall reading that some medical research journalist wrote that a person's insulin can go up even just by thinking about eating a donut. The body expects or anticipates a glut of sugar, so it tries to prevent it preemptively.

I think the migraine is triggered by a bout of low blood sugar due to my body thinking that the sweet-tasting coffee is loaded with sugar. So when the insulin enters the bloodstream, it drives blood sugar way down.