lost worlds

 I keep getting messages that there was a problem loading this world and I have to start  over from the beginning but it is still the same time of day.  Now when I make copies that also has the same issue.  Just now I died and I got respawned back to the beginning.  this has been going on since June.   Can I please get some answers?  I"m lucky too have a world last for three weeks anymore and it is getting to the point to where it is pointless to keep playing.