Protruding vertebra...??

I noticed a few weeks ago that my spine is a little sore to the touch about half way up my back. Not terribly painful, but sore as though I'd knocked it. Yesterday I glanced into the mirror as I was getting a shower after running and noticed that a vertebra is actually protruding from the middle of my back!! Not by miles, but very noticeably. I bounced this off a member of my family when I got home, and they immediately noticed it too (w/o prompting). I'm going to get it looked at asap, but in the meantime does anyone know what this might be? I can't help feeling a little alarmed! I don't have a history of back problems - yet... :-( Any light you can shed will be gratefully received.