Because I always forget the name, I had to go and look it: anomic aphasia. I noticed it happening a little bit when I used to take topamax for my migraines (it was actually worse on depakote, which caused me to switch wrong words right into the middle of sentences without even realizing I was doing it; think "I'm baking the football now", for the couple of months I took it .. frightening).

I didn't notice that effect getting any worse over time with topamax though, and it may even have gotten better or maybe my mind found a way to work around it. While I wouldn't suggest you ignore the effect, if you find the drug otherwise helpful to you, or think it might be, you might want to wait it out. It worked especially well for me, for a long time, but did eventually stop being effective towards the purpose for which I was taking it, so I stopped. Otherwise I would still be taking it, even with its faults, as working solutions for my hellatious migraines are hard to come by.

Good luck.