What Causes Upper Abdominal Pain And Severe Diarrhea?

I have been experiencing upper belly pain and sever diarrhea for a week. My meds are also going straight through me. nothing is being absorbed. And yes I have seen the undissolved pills. I cannot eat anything with out hurting and running right through me. Not sure if I should just wait it out but the stool color changes from black and tarry to light. Any answers?