Hi - The only way I can tell if I'm having a particularly bad odor day is other people's reactions, unfortunately. Sometimes when I'm at the grocery store, I will intentionally stand near someone who is looking at stuff on shelves. I just pretend to be doing the same thing. If after a few seconds, I don't get any reaction at all, that's a good day. If I walk by people or they walk by me and don't cough or sniff or make a face, things are fine. If I am talking to a person who is a normal distance away and they don't back up, that's also a good sign.
I can smell my odor in a room I've been in if it's all closed up. It is a good day if I can walk back into a room that I'd been in for a while and not smell anything.
I don't know if that helps you at all, I hope you are one of the lucky ones, and you really don't have this to deal with.