My little ZsaZsa had the same problem, bad breath. Ooooh it was like she had been in the toilet bowl. I took her to the Vet and she stated that my little baby had not lost her puppy canine teeth and that food or hair can build up there. She gave me an antiobiotic for her. I brushed her teeth often and would slightly play with those teeth to loosen them. One of them has already fallen out and I can tell a big difference already. Some Vets remove the teeth themselves but they put them to sleep and the anesthesia can be dangerous to a 3 lb yorkie. Use your own judgement and talk to your Vet. This may be part of your dogs problem too. I hope this helps.
