I Am A 54 Year Old Male. Recently Had Flu-type

I am a 54 year old male. Recently had flu-type virus. Lots of hard coughing trying to clear lungs. During several particularly severe coughing fits, an abdominal muscle bulged out over my lowest two ribs. Not the diaphram, but directly adjacent, sometimes left side, sometimes right. VERY PAINFUL. Today it happened while I was crouched down at work (I was installing tile flooring). Google's no help. Who better than the prestigious Mayo Clinic to have the answer?