depends on how often you take it.
With many migraine drugs, it us pretty usual for the migraine to come back - actually if it doesn't come back until the next day, you are lucky ! Mine usually comes back about 6 hours after I take the first dose (I use imigran) - so I just take another dose. That usually gets rid of it and it doesn't come back, until next time.
My neurologist tells me that I shouldn't take more than two doses a week of any vasocontrictor drug designed to treat a migraine attack. Two doses a week or less and then I should avoid any rebound headaches. The return of the migraine 6-8 hours later is not a rebound headache - it's the same migraine returning. That is pretty normal (my neuro specialises in headache and says this return is to be expected).
So, if you are taking more than two doses a week, then it may well be a rebound headache. But if you are only taking two doses a week or less, then it's probably not a rebound headache.
Sounds like you need to talk to whoever is treating your migraines for you.
If you are getting lots of migraine, there are a whole bunch of migraine preventers that you take daily that really work. I am on tofranil, which really reduces the number of migraines I get.
good luck with those headaches
raglet