I never had covid,and always tested negative and dont have any mercury fillings. But I still think that I may have gingivitis because sometimes the back of my gums bleeding when I floss.And I didn't get a bad smell on my floss after flossing.I don't take any medication either .if the back of my gums bleed when I floss and I have a metallic taste and the back of my teeth are receded It must certainly be gingivitis.