My 30 year old husband has severe right side pain in lower abdomen and back and now has blood in his stool?

A few options: Infections, meckel's diverticulum, diverticuar disease, appendicitis, etc., "could" cause the symptoms. Any of these should be evaluated in the er, likely get a ct scan/labs, and possibly a surgical consultation. Go to er for evaluation.

Emergency: Take him to the emergency dept immediately. This is a crisis that requires immediate medical attention. It won't get better on its own and time is important. Good luck!