Rat is losing weight.

Question
I got my rat, Tasha, about half a year ago with her sister, Sandy. I also have a third rat I got before those two, Lola. I bought all three of them at petsmart after having to take two others back to Petco, which didn't seem to take care of their rodents very well. Petsmart on the other hand, contrary to what I've heard about getting rats and such from them, treated their rats very well. However, about a month ago Tasha started acting funny. She was very lethargic and was hardly moving one day when I got home from school. So I called up the exotic animal vet and took her in right away. It turned out she had a respiratory infection, so I seperated her and gave her the medicine the vet gave me until she got better, then put her back in the same cage as the other two, who thankfully didn't catch anything from her.

Since then, she has been acting fine, eating, running around and playing, like a normal happy rat. But, shes been losing weight like crazy. I can see her ribs poking out and the top of her hips, and shes super skinny. I felt along her belly for any sort of ulcer or tumer but was unable to find anything, and she didn't cry out. I'm not really sure what could be wrong with her. Any enlightenment on what might be wrong would be very helpful. I love all my pets but surgery for a rat would just be too much as I am a senior in high school and even with my job would be pretty much unable to pay for anything extreme.

I'm not sure if her illness has returned or if she has a tumor or something. She generally acts normal but I just cleaned her cage and it upset her a little I think, she's just sitting still in my lap, whereas the other two would be running all over or climbed up to my shoulder. I'm really worried so any information would be helpful.

Thank you,
Korri

Answer
It could be chronic myco.  How long was she on medication for? Of sje was not treated properly, she could become chronically ill.

How sure are you that your vet was exotic certified?  Alot of them say they see rats but that doesnt mean  anything.  

Check out my site, sandyscrittercity.com and refer to the page on MYCOPLASMOSIS.  See if she was treated the right way....let me know soon as you can.