TLDR all my items gone after re-entering world

Every time I play survival and exit the world, my items disappear. Ex. I put all of my items in a chest and then left the game. A few hours later, I logged on and a majority of the items were missing (all of my stone materials, gold, enerals and weapons) another occurrence of this is when I have died AT SPAWN none of my items remained and disappeared. This is incredibly infuriating. My most recent world I lost an abundance of materials that would have allowed me to finally beat the game. Please help