How this happened: I deleted my world that i was working on for 12 days.  I was very mad and didnt play for days then i decided to go back on and i went to create a new world and typed in "World 3" That was the same one as my old one.  I spawned and noticed that there was a torch next to the spawn.  At first i thought it was a glitch and then noticed that they were leading somewhere.  Then i noticed the exact lava river i made. I ended up finding my old base that i made.
 
How this works:  I dont know if this would work for everyone but if you delete your world try to type the exact name as the one you deleted.  Also leave the seed blank.
 
Note: I never backed up my game at all.