My sister gets extremely bad migrains and she has a trigger for it. It's actually cheese. She can't eat a grain of cheese, or even traces of it in anything (and I mean anything). She has to read every ingredient on every item she buys, the smallest amount will set it off and she's gone through a million tests. It ususally affects her the day after she's ate it and by bad I man she often loses her sight, she pukes and she's usually lying on her couch for 24hrs+.
She has blood pressure pills and everything in between but when we were kids we had a tobogganing accident, we hit a tree going down the hill and my sister was on the front. She hit her head, cracked her jaw, broke bones, etc. etc. It was the worst incident of my life to be in but it was since then that she's had the headaches.
I don't really have much to add, but narrowing it down to what triggers the headaches is extremely important and often hard to diagnos because it's usually not a food allergy.