Saved changes when using Word

Hi,

I recently started typing a lot of work reports through MS Word that I save on my laptop. When I go to close the document it asks me if I would like to save the changes I've made. The thing is, I haven't changed anything, at least not to my knowledge. I've started to click the edit button to see if I can actually undo the changes but most of the time it reads "can't undo" other times it closes without asking me to save. Does anyone know why this happens? Thanks