Moonshadeau, knowing you personally, I wonder if your youth may be one of the reasons you were passed over? You've got the smarts, the brains, energy, personality, and the ambition, but in some hospitals you may find that no one under- say, 30- is considered for any promotions (even for a straight day position!) just because of their age! Especially in hospitals where the docs "rule" the place!
Sorry I didn't see this sooner; but don't just email a thank you: a handwritten thank you would be remembered much better and would help in future job applications. Handwriting a thank you shows extra effort and I think some maturity on the part of the applicant, too.
Good Luck, Kiddo!:)