What Could Cause Burning Sensation On Shaft And Head Of Penis ?

48 yr old male.Dealing with burning sensation in shaft and head of penis. Had urinary frequency and pressure however that has subsided about 75%. Had urine test done, blood work all negative. Had anal sex with wife 3 days before this started. Yet Dr cant find anything. Feeling desperate. Not very confident in our lab techs as they have had several issues with not performing blood and urine tests properly and not to the recommended length of time for urine cultures.I live in a remote little town in Canada.