Unable to build in Single Player mode

Hi! My Minecraft has been like this for a while, where I can go into a world destroy a few blocks, exit the world (or launcher even) and go right back in and the blocks will be back and I will be where I was the first time. I have tried moving 100-200+ blocks away and still... I re-downloaded yesterday and it still did it. Please help me D:

P.S It does it for all world even new ones... Multi-Player (like a LAN) works perfectly fine.