Smelly penis

EDIT: we live together i wash his clothes and he changes his underwear once or even twice a day.

EDIT 2: We still have set i make sure he is wearing a condom

Edit 3: he baths every other day or everyday depends how sweaty he gets he washes his duck properly by pulling the foreskin back and washing it and he pats dry the area. Even washing straight after the smell is till there.

Edit 4: I don't think its an infection he isn't red or sore or having any problems down there what infections can it be

My boyfriend wants me to go down on him but his dick smells really bad I'm gaging just being close to it.

He has good hygiene and has been tested for all sti and std but all come back negative. Even after washing his duck the smell is still really bad. What can be causing it and how to stop it smelling anno they do have a duck smell but this is worse and not normal