I used to have migranes every two weeks on average but they stopped when I switched from a western diet to pure vegetarian ("vegan") diet some time in May last

I used to have migranes every two weeks on average but they stopped when I switched from a western diet to pure vegetarian ("vegan") diet some time in May last year. I'm not 100% certain it's the diet (how could I be?) but I can't ignore the causality.