She or he may have kennel cough which is common in puppies. I have a 4 month old yorkie and she has kennel cough. I suggest you should take him or her to the vet I hope this helps
My Tea Cup Yorkie Keeps Coughing And Sneezing, Can You Help?
The air probably isn't clean.
I don't know just taker it to the vet : ) thats what I did and she is fine now