Could be any number of triggers with the migraines.
I used to get them every Tuesday evening (that was my 'Sunday') because I would go to Louie's in Ballard and get the duck. It turned out that back then (at least) the duck was loaded with MSG. So, I would trigger the migraine just as my weekend was ending. It was considered very suspicious at work!
I also used to get migraines as a result of sleeping later in the day on weekends. I would suspect that would tie in well with the neuro-adaptation to stress, or rather, lack of motivation for the serotonin to get up to speed.
Keeping a diary of the migraines may help. Miserable little things

. Getting back on topic somewhat--there's no way I would be able to ride in to work with a migraine, especially if it was one of the fortification episodes.
East Hill