What Could Sudden, Strange Smell Of Feces In Nose Indicate?

Sometimes for no apparent reason (there is no sufficient source for the odor), I have a strange smell of feces in my nose. most of the time, it goes away, sometimes it lingers. It's hard to differ between a genuine smell of poo that's really there, like for example if someone stepped in a pile of dogshit, or if I'm having one of the aforementioned episodes. I'm pretty sure I'm the only one who can smell it. It makes me kind of paranoid if I washed my hands properly after leaving the toilet. What could it be?