Losing items and progress while at any time

I have had no problems with crashing or visible malfunctions. The first sign something was wrong was when I went to play my 2nd time and the 1st world I had created and played in for hours was gone. Totally gone. I figured maybe I was confused or something so I didn't report and just start to play again.
I collect lots of items(nothing too fancy), and I build a bridge with a fence on it and then I move onto to do something else for maybe 20 minutes. I come back and part of the bridge is missing and other things I had done were also undone.
After 4 hours of playing, I save and quit. I got on the next day (today) and MOST of my items are gone.