What Cause Severe Pain In Back And Under The Breasts After Delivery?

I am a 24 year old female, 5ft 7in, 208lbs. I just gave birth to my first child on March 31, 2011. I have been having "attacks" of pain that is constricting & taking my breath away. It's in my back, behind my ribs, & wraps around to under my breasts. It makes it really hard to breathe or even take deep breaths. What could this be?