My Husband Has Had Diahrea For 3days With Stomach Pain

My husband has had diahrea for 3days with stomach pain & lower back pain with a feeling of nausea & it is not easing with the use of Imodium he has had bladder cancer in 2016 x2 opporations with cancer taken & the last clear the chemotherapy is put into the bladder at the time of the opperation no other treatment also is type 2 diabetic & has in 2014 had a 4x heart bypass . Would this be or could this be anything more than a bad bug or virus?