Can i undo something i did yesterday on Wordpad?

[Asia]

So i was writing something on Wordpad and every now and then i would just add more and more i wrote a little more last night then when i got on the computer in the morning half of the document was gone not just everything i wrote last night but like stuff i wrote weeks ago and saved are GONE.. whats the reason for this? Did i do something wrong i didn't notice? is there away i can just undo everything i did yesterday? can i do anything to get it back? help would be much appreciated =]