Welcome! I'm sorry to hear about your struggle with migraines. As you said, it's something we all struggle with on this forum.
It sounds like you're on the right track to figuring it out. Unfortunately as you're learning it's a long and arduous process. As you read in the Heal Your Headache Book many neurologists believe in a headache threshold. So while a food, preservative or envrionmental factor may trigger you one day it may not another.
I have found that preservatives and MSG are my triggers. I found that my husband and I were eating many ready made things that come in boxes, frozen or out of packages. Once I read the book Heal Your Headache I was able to tell what was in them that triggered my headaches.
I have also found that yeast is a trigger. Yeast helps food expand and also seems to make my blood vessels expand. I found this with the help of a naturopath and an elimination diet. Be careful if you try this route, they will tell you to cut out milk, wheat, sugar and often meat. I can't live on that restrictive a diet. I cut out what I was sure triggered me and eat what I know doesn't. I have found that as long as we make it from scratch I'm pretty good. I don't eat bread because of the yeast but do have wheat in other things. A naturopath will tell you to stay away from white flower but I hate brown so I cut down on the amount of white flower. I drink milk though am cautious about sinus headaches because milk causes phlegm.
You said you haven't taken preventatives for 12 days, do you mean over the counter pain medications like Advil. I ask because when you said you were taking 4 Advil a day that can cause rebounds and interfere with Topamax.
Have you considered environmental factors? Certain smells bother me. Rain storms trigger headaches for me and I can't do much about it and stress is another trigger.
As for the Depo-Provera, it is preferred for migraine sufferers because it doesn't contain estrogen, but it can trigger headaches. What about other medications? Are there any others you're taking that can trigger headaches?
And finally, how is your sleep? Do you sleep well? Do you sleep through the night? Does your schedule vary a lot? Any of these can trigger a migraine.
Hope these help a bit. Keep in touch and let us know how it goes.