So glad to hear that your doc is willing to work with you on finding the right meds. Sssooooooo important!!
I have not tried Topamax, but many, many others have. One of the side effects is that it CAN cause cognitive issues. It can make you feel like your brain is not cooperating. Do not let this hinder your attempt at using it. The side effect does not hit everyone! You may find that it merely gets rid of your headaches!
Before I had my shunt installed, my doc had me try many different meds. I kept a log of how each one made me feel, what dose I was on, etc. There are really good forms available on this website, including a medication log. I highly recommend that you use it. You may find that as you increase the dose of a certain med that it makes you feel worse where as a lower dose worked well. Having this info in the log will help with that.
Again, many folks have used Topamax with good results, so I hope you will find the same.