One prescription medication that is specifically intended for treating migrane headaches is "Imatrex" also known as "Sumatriptan succinate" or "3-[2-(dimethylamino)ethyl]-N-methyl-indole ¾ 5 - methanesulfonamide succinate".
I'm surprised your doctor hasn't tried this yet. Imitrex isn't for everyone: maybe he ruled you out for some reason. ASK HIM.
Imitrex can be administered by injection, nasal spray and pill. The injection works fastest, as you might expect. People who have used it say it turns off the migraine like turning off a light.
Something else you might want to consider as an herbal headache preventative is feverfew. It will take a couple of weeks before it begins to work, but users report less frequent and less severe migraines when they are taking feverfew.
Mulan is right about dehydration being a possible cause. Many people have found that diluting Gatoraide 50% with water works better than full-strength Gatoraide. You could also try using an oral rehydration formula:
½ teaspoon salt
1 teaspoon baking soda
8 teaspoons sugar
8 ounces orange juice
Dilute to 1 liter with water
This "recipe" is one that everyone should have written down somewhere for emergencies. The sugar and orange juice are there to make it taste better.