Why do my migraines always start in the late afternoon roughly every three to five days?
Most likely it's a trigger of some sort that you encounter on those days or, with some triggers, up to 48 hours earlier. It could be a food, fumes from cleainig products, or any number of things.
Try logging what you eat, what you do, your sleep schedule, the weather, your exercise, etc., and watch for a pattern.
I have noticed that I usually get migraines between 2 and 4. I know this doesn't fully answer your question, but I think it has a lot to do with my blood sugar. I used to eat my biggest meal for dinner, but recently started eating a bigger meal for lunch - and earlier. It has helped some.
A lot of times my HA start (I have chronic daily and migraine) that time of day too. I think it's because that's the "witching time" in general. Well known for babies and little kids to be cranky then too. If I'm at work, I'm stressing about finishing up so I can leave (and leave with a clean desk since I only work PT) and then knowing all the stuff that awaits me at home - dinner, homework with the kids, mail, animals (we have a little zoo of pets) to take care of, baths, baseball, karate, etc, - just the whole stress of so much to do in so little time. If I'm at home, even though the kids get home from school at 2:30, it's the same thing and I'm usually running to more places AND feeling guilty b/c I didn't get everything I wanted accomplished that day. So late afternoon is just when your body has said enough, but your mind is ramping up about the evening.
I never felt "anxiety", though I have felt stressed out at various times since college (usually expressing it with stomach pain), and after going to my "yearly renew my meds, maybe make a little change" appt with my PCP last fall, he actually took an interest in what I was telling him and made me come back in 6 weeks after making a big change in my meds. He listened to one little thing I said about grinding my teeth and asked me if I'd be willing to try antianxiety medications. My migraines started when I was pregnant with twin boys (and now flare up around my period so I know they are hormonal too) and the CDH started when the kids went to school and I had to make a decision about holding them back b/c 1 had learning issues. Let me just say, it was a lot easier to deal with a burning stomach all thru college than it is to get control of this 10 lb pain on top of my shoulders! But with my PCP's patience, we've made a lot of trial and error changes over the last 8 months or so and while my medicine cabinet is FULL, I think we're finally on the right track.