Like Nan sez, even tho we like them, a lot of us shorten our unusual names in everyday use to avoid having to repeat the same dumb explanations. I even list mine as "David" in our company e-mail address book because policy says you've gotta list a full first name and as often as people misspell "Daividh", my messages would NEVER come thru.
Have you ever thought about beating the nicknamers to the punch and just going by Lib or Libby? People that don't know you well would assume it's short for Elizabeth, and if they're wrong, so what?
Hang in there! It gets easier once you're through school! :)