No need for a vet visit. First, if you are using pine shavings for bedding- get rid of it now. That could be part of your problem, the oils in it can irritate the respiratory tract causing infections to crop up. Second, I am pretty sure you have a feed and grain type store near you, the type farmers use for stuff. Go get the teramycin powder (antibiotic) thats used for chickens, it should cost you around $3 maybe a little more little less. Mix 1tsp of the teramycin to the rodents water (in thier water bottle) to every 4 ounces of water, be sure that you cover the water bottle so the contents are kept in the dark, change DAILY. You must have the contents in the dark b/c light destroys it. Treat for up to 10 days.