My Husband 73 Healthy Male Has Had A Intermittent Fever

My husband 73 healthy male has had a intermittent fever for 2 days. It goes from 97 to 100.4 F. Advil helps. This has been going on for 3 days now. He has no other symptoms except for the occassional chills. He had prostate surgery 3 times, but the last was a complete " coreing out of the prostate and removal of 3 walnut size bladder stones. The last surgery was over 3 months ago. He still has urinating problems ( going alot) and wearing a "diaper" .