Cramps, bloating, inconsistent stools

Iam a 47 year old male. For several weeks now I have had abdominal cramps along with brief periods of pain just below the right side of my ribs.The pain radiates into my back as well.I have also been experiencing incosistent stools from bouts of constipation that last one to 2 days to multiple days of loose stools where I may visit the toilet 4 or 5 times in a day. The stools had typically been light to medium brown.For the last 2 days my stools have been frequent and VERY DARK brown and soft.This concerns me.I have been drinking Pepto Bismal for the last 3 or 4 days due to the cramping. I have a very high pressure/stressful job,and tend to worry.Any suggestions?
Dave

The pepto will make your stools dark.