Harvey had the sniffles so we took him to the vet. Luckily we were able to find an exotic vet much closer to home. I'm so glad we took him in because it turns out what I thought was just sniffles was actually pneumonia. After doing some research, pneumonia is the most common cause of death with guinea pigs.
As you can see, his lungs are very gray. The vet said that there should really be more black. The gray means there is fluid in his lungs.
We have him on antibiotics and also probiotics (strawberry flavored Activia). I completely changed his environment so that hopefully he isn't surrounded by the bacteria that caused this in the first place/Biscotti's stuff.
Below is an X-Ray of Xabi. As you can see, his lungs show a lot more dark space (air).