I was on Topamax for 1 year, the only side effect I had was curbing of my appetite, which is a good side effect!
However, it never did anything for my headaches, and when I was weaned off it, I think I was taking 150 mgs.
My current neuro, who is probably the best in his field, told me if Topamax didn't have any effect in the first 3 months, I should have been weaned off it. He had me wean off it, and my appetite came back.
Have you been tested for sleep apnea? Many people find great relief of their headaches once their sleep apnea is being helped.