My husband has a bulge on right lower abdomen causes pain sometimes. went to hospital did ct scan, blood and urine test all normal. what could it be?

Sometimes: an abdominal wall hernia can be present only when standing or doing things that increase pressure in the abdomen (coughing, lifting objects, etc.) The hernia may not be seen while lying down during a CT scan. Ultrasound may detect these hernias if done while the patient is upright or performing the valsalva maneuver (increasing abdominal pressure).