Medications How long should my pig be on antibiotics?

I have a female smooth,short coated guinea pig purchased in September from Petsmart. I'm guessing she's almost a year old. She is our first guinea pig. When we brought her home she seemed healthy, but she did seem to make a puff sound occasionally. It wasn't a sneeze and it wasn't a cough. Gradually she seemed to breathe more heavily. Her eyes and nose were clear. We took her to a vet who saw guinea pigs, but not an exotic specialist. They said she looked and sounded fine, but thought maybe they heard a sneeze and based on our data, prescribed baytril. After 7 days (+ probiotics) she didn't seem to be any better or worse. We figured it was just her normal. A few weeks pass and again I'm concerned she's working to hard to breathe. We take her back to the same vet. They say her lungs sound clear, but maybe she has some blockage or growth in her nose and suggested we take her to an exotic specialist. We take her home and wait a week or two to see what happens. This time she definitely declines, but still eating and happy (just less active). So we take her to an exotic vet. They diagnose her with pneumonia and put her on baytril, reglan, and acidophilus for two weeks. At the re-check she is barely better, but the vet says her lungs are clearer and prescribes another 2 weeks. Not sure if she really improved this time, but vet says she's getting better and prescribes another 2 weeks. We are now at the end of 6 full weeks and our pig is definitely not worse, but definitely not popcorning, and still seems to breathe heavier than an animal should. So, is there a chance she'll ever get better or am I destined to pay a vet bill and medicate her for the rest of her life. I know to avoid a pet store purchase now, but their aren't any rescues in my area. If this pig doesn't make it, what are the chances that I can actually experience a happy healthy pig. I'd love to get 2, but I'm now more afraid that the vet bills will be through the roof. Thanks for reading and any insight you can provide