What about Omega-3 Fish oil tablets dissolving in you glove compartment, or under tour seat from heat.
I often got a whiff of rotten fish throughout the day, sometimes at work, home etc. I used to think it was my wife, then I thought ah, my coworker. But later realized it was me. The cause? My jacket had a dissolved Fish oil tab and washing it didn't help. It was a faint smell that was hard to locate.