coming down from stress. As in, I won't get one if I'm stressed out but as soon as I relax (like after an exam, or if I've been stressed planning something as soon as that something is actually happening), I'll get one.
None of the prescrption drugs to take once you get a migraine has worked for me. Imitrex just made it worse. Excedrin Migraine with a LOT of water seems to help a bit.