Does it smell kind of like rotten blood? If he's teething then that smell is normal. Just check his gums to make sure they're not swollen and red and no teeth are impacted. Make sure he has alot of chew toys. Also, I wouldn't suggest giving Greenies to puppies younger than 6 months, or while teething, they can pull the teeth out. You could always try doggie toothpaste, but when my pup was teething nothing seemed to help. It should go away in a few weeks.
Both right... It's just teething breath. Chino is five months old, no impacted teeth, but has been teething left and right and his breath smells like blood/fishy and its not very pleasant. the more you let him chew, the more it will probably smell, but the faster more teeth come out.Just sounds like bad breath from losing and gaining teeth. Once all thats is done his breath should go back to normal. Just keep letting him chew things, thats is a big relief for pups and achey teeth.