All my stuff is gone in minecraft?

Ok so I went into the new update (1.8) and checked out my world. Then I went back to 1.7.10 and went to my world then I went back to 1.8 and all my stuff is gone… Like my armor food and supplies and everything. Then underneath all of my minecraft signs there are words tht say null… What happened? Will I ever get my stuff back? I'm really freaked out:/… This is a single player survival world btw.

Sounds like you went to the older version, and saved which would eradicate anything after that version. Doesn't sound like you're going to get it back.

I have a pe creative mode world with lots of effort put into it. I went onto it and nothing that I built was there. Why?