Q. Lots of sneezing with mucus, bad breath,14 yr old male
DESTINI R. HOLLOWAY, DVM
A. It is possible that your pet has severe dental disease that has a lot of bacteria in the mouth that has now translocated (moved) from the mouth to the sinuses/respiratory tract.
I would recommend that you get your pet a good physical exam by a vet and an oral exam to evaluate the teeth. The canine teeth, in particular, if they are infected underneath the gum and have eroded away at the periodontal bone, then they can create a fistula (hole) leading directly into the nasal passage causing irritation (in the form of sneezing). The irritation eventually can lead to respiratory infection and possible pneumonia if not corrected.
If there is infection found then the only fix for this would be to start on antibiotics to get some of the bacterial load down about 3-4 days before scheduling a dental cleaning and most likely teeth extractions to remove the source of infection. If the teeth are the problem they most likely have to come out or you are just swimming upstream with oral antibiotics to no avail.