Hi! Welcome :). You were just recently diagnosed with migraines, or 15 years ago you were diagnosed with migraines and they've continued for 15 years?
It sounds like the drugs you're taking currently are just to take care of the pain when you get a migraine. You need to be careful with how often you take these drugs, because if you take them too frequently they can cause "rebound headaches". This means that the drug may relieve the pain when you get the migraine initially, but actually cause another migraine later. You can talk with your doctor about how often you can take your medications, and how to prevent "rebound headaches".
There are also drugs you can take daily to prevent migraines. Topamax is an example of these drugs (which I'm thinking is the drug you're referring to when you mention "topomac"), but there are many options for preventitive drugs.
Are you seeing a neurologist that specializes in migraines?
As for your specific question, I have to admit I don't know the specific answer to that, other than to say you may want to google the drugs you are curious about and look for studies that look at prolonged usage (I've been particularly curious about prolonged usage of topomax, myself).