It happened to me recently, in a different context, when I was logging in from my phone. For whatever reason, Facebook seemed to think I was logging in from somewhere rather a distance away from where I actually was. I never changed my password, and the alerts matched known usage.
I don't know if you'll need to change your password so often; the most sensible thing to do is keep track yourself of when you are logging into facebook, what device you are using, and where you are at the time. If that matches roughly what Facebook is saying, it's probably just you but tracked badly.