I Have A Constant Ache In My Entire Belly For

I have a constant ache in my entire belly for the past 3 weeks. Nausea, diarrhea, but no vomiting. The pain is so intense I can't sit still for long and laying down is torture. It feels like my guts are in a knot all the time. The pain is worse at night and better with narcotics which I take for my back and knee.