We took some great photos with our friends on the beach. We were using an older Nikon D3100. My girlfriend, who was the one who took most of them, noticed that a few of them were missing. She thought our friend had deleted them because she didn't like them.
We went through them that evening - right in the camera's gallery - and everything seemed fine. The next day we took some more photos while sightseeing, and after that none of our beach photos appeared. Not in the camera, not on the SD card, and they weren't found by Disk Drill or Recuva either.
My question is - what could have caused this? And how can I prevent this from happening again? Should I get a new SD card?
Any help would be greatly appreciated.