It could be related to the nerves that process smell and taste. It's always a good idea to talk to a doctor when your senses change, as it could be a symptom of a bigger problem.
is it your stomach? Do u smoke anything? are u a big meat eater? have you changed your diet or supplemented anything new to you regimen?
Do others tell you you have bad breath? I've been around chronic halatosis people, some inherited it some had diabetes, etc. Others have stinky yawns and breath coming out of their throats from coffee. if it's new to u ask others if they've noticed before you.