Is there something wrong with my camera?

It could be your memory card. Mine does that occasionally, it overlaps pictures that are either on the camera, or have been deleted off the camera. I would format your memory card, and that should help fix the problem. You might just have to buy a new memory card, that will guarantee a fix if formatting it doesn't work. Make sure you get all your pics off your card before formatting it, as it will delete all photos.