What Causes Blood Behind Navel After C Section?

I had a C section 8 days ago and for the last 2 days had what appeared to be blood behind my navel. There were some obvious broken blood vessels around my navel and it became slightly hardened. since yesterday it is getting better and 'browning' and is now just looking very bruised around the area. This is several inches above my incision. It is soft again today. What would cause this?