Bad taste, Bad smell

1. Dental problem, most likely, especially since you mention smell.

https://health.clevelandclinic.org/2...in-your-mouth/

There are even more rare conditions not on the list. I worked on a study once of a certain brain surgery, and hitting the wrong spot can cause such a taste, permanently.
I think I have heard of the also really rare such taste resulting in a heart attack or stroke.