I'm having the same issue. It started after I updated to lollipop 5.0.1. No issues using Facebook on my laptop. I have tried uninstalling and reinstalling the app, cleared cache, force stopped the app, rebooted phone.. Nothing seems to be helping.
Have you tried using the browser in your phone? If you can access your FB with Chrome, for example, there's a workaround until the app is fixed. Open your FB page and create a shortcut in your homescreen.