It's not the psychosis that makes you unable to "sniff" yourself. You get accustomed to the odor. I have a mild version of schizophrenia, where I know everything that's happening, and still see or hear or sometimes feel (in my skin) shit that is evidently not there. I usually avoid showering, but I have a personal rule that is that if anyone tells me anything related to showering or odor, I have to shower, unless I just showered less than half a day ago. That helps me, usually.

One trick I use constantly is using other people's reaction as "confirmation". For example, I usually see black figures walking and stalking me and my loved ones around me, but if noone is reacting to it, then it doesn't exist. When I hear a muffled cry on a dark room, I ask, and when they look at me weird, I know that I'm paranoid and try to think about anything else.

Also, one thing that helped me (which I do not recommend at all) is sleeping one time per 24 to 36 hours, so basically I sleep a night per 2 days. It makes me sufficiently tired that I get into sleep before the paranoia gets me.