You need to take him to a vet to be checked out. Short-nosed dogs like Pugs can have a hard enough time breathing as it is. And anything which makes this a great deal worse, can actually end up as a life threatening situation.
He may have a 'collapsed trachea'. I am not saying he has of course. I can't tell. An X ray might help to see if that's happening.
Please do take him to be examined.