Try doing a hard reset - push/hold home and power button until white apple appears (ignore anything else that shows on the screen until then), let go. Often this will take care of weirdness.
Might have to do it more than once and it should be done periodically, especially if you've made a lot of changes or downloaded/deleted a bunch of apps.
However, if this doesn't work, check to see how many apps you have open (double click the home button). If there are a LOT of them showing, touch/hold one of them until they jiggle, touch the "-" sign to close out all but those you are currently using. Check this periodically.
The third possibility is one of your recently downloaded apps may not be playing nice with either the iOS or other apps. If none of the above work, delete your most recent apps until the issue goes away. Then reload the apps and watch if it shows up after each is added. PITA, but sometimes the only way to identify an offender.