Try to reboot your phone and test it again, if all else fails, a software restore might do the trick. (Make sure your files are backed up) To do it you need to have a computer that has an iTunes program. Turn off your phone, then before you connect it to the computer via a USB cable press and hold the 'home' button, don't release it until you see the iTunes logo on your iPhone. Next, open iTunes on your computer and select restore (this usually fixes most of the software bugs you may encounter)
Hope this helps!