I have the exact same problem! It occurs when I floss my upper wisdom tooth which I still have at the age of 69. It really turns my stomach. I brush my teeth and test if the smell is still there so it never goes away. I also have a peri - rinse that was prescribed a long time ago and I have used that to no avail. I do not have a filling in this wisdom tooth but there is one in the tooth next to it that is about (truth) ten years old.
Seeing a dentist is advised.