I am a 31 years old male in good health. Around 2 weeks ago I hurt my back (middle/left). I went to the chiro, and she adjusted me and said a rib probably popped out of place. It was feeling better until yesterday when I was picking something up. I hurt it all over again, probably worse this time. Today I noticed a sizeable amount of blood in my stool. What could be wrong and what should i do?