I get that smell a lot.  Only I seem to be able to smell it, my family doesn't notice. Sometimes it's the ammonia smell (like pee with the pee in it, I don't know how else to describe it) and other times it's the sweet cloying scent of something just as it starts to rot (that's the best description I can come up with).  In both those cases it's my nose itself.   For me it's always sinitus or a nasal infection , and it's usually caused by something else like a throat or chest issue.  Go see your doctor, get them to do a strep test.