Hi, try switching the vibrate on/off a few times and have a mess around with the settings. failing that turn the phone off and back on again. If this doesnt work, then connect your iPhone to your computer and see if any upgrades are avaliable, once upgraded it might of fixed your problem.. If there is no upgrade to iOS, then back up all your files and restore. If this doesn't work, request it to be repaired by apple. They will send you a box and everything to send your phone off to them in. They generally send you a new iPhone! Good Luck fixing your problem!