Try a hard reset ... hold power and home buttons until the white apple appears, then let go.
If this doesn't help, you might need to reinstall the update - a clean install, as it's called where you do a full restore. PITA, but usually gets rid of weirdness.
Another possibility - one or more of your apps may be having issues with the update, particularly if you have an app that runs in the background - like a weather or news app.