So I have a Macbook and use it for the laptop program in school. Recently (3 different times with 2 different files) it has been deleting my saved work. I would work on it and compete about 3 slides, save it and exit it. Now, I just re-opened the file, and it doesn't have any of my previous work on it. I am 100% positive that I saved it.

Can someone please help me?

Any information will be very appreciated.