18M - Penis hygiene

I have been having problems with the odour of my penis for the past 1-2 years, I just turned 18 and I have been sexually active since I was 16 and the tip of my penis has been smelling like fish, even after showering ( I can also smell it in the shower), washing it every day, but it still isn’t going away. I’ve talked to the doctor twice about this problem and I was sent to get tested for std’s and both times the results came back negative.

TLDR: I have good hygiene, I don’t have stds but my tip smells like fish