I've had the same thing occur to me once - I came down with a pretty severe cold and was coughing/sneezing a lot. I think the pain in your ribs is caused by muscle aches (like when you work out a little too much). Personally, I didn't really think much about it and it went away after my cold went.
I could be wrong though - if you think there's something more by all means get it checked out.
2004 Camry Special Special Edition (Van)
1997 Mazda Eunos 500 (Oz) (Sold... obviously)