Pug breathing becomes so labored it’s frightening

My pug is a neurtered 2 year old female who is about 5 pounds overweight. I try to take her for walks, but her breathing becomes so labored it’s frightening. It takes her a very long time to recover. Our vet can find nothing wrong, but I wonder if she might have an elongated palate that is making it difficult for her to breathe? I’ve done some research and this seems to be a problem with some pugs. Please answer as she is the sweetest dog and I paid a great deal of money to rescue her from an abusive situation.