Lost all my work

I've been losing many hours of work with cars/engines. Yesterday I lost a whole engine series that I spent most of my Sunday on
. I created the engine family and after each revision I would close the game after clicking on "X" to the main menu and then clicked on "quit game", I was checking because I wanted to make sure I didn't lose my work. Of course, I finished my final revision for the day (2nd revision or 3rd revision) and decided to pack it in so I could watch the hockey game and I lost ALL of my engines. Not just the revisions but the entire family.
