Kirsten, I'm so sorry to hear this. I sure hope that the pain meds will be able to continue to help her. I've also had overweight cats in the past and my Radar is still currently overweight even though he's a very large cat. You just need to make sure that cats don't lose too much weight too fast or else they can get hepatic lipidosis which is fatty liver disease. My RB Pepper got this when he became very sick which made him lose a lot of weight very quickly. I hope that Lily will stop trying to attack Luna. Cats can sense when another cat is ill or weak and then they try to bully them. Since x-rays won't be able to show anything, did your vet ever mention doing an ultrasound? Maybe this would be able to show something. Lots of prayers and positive thoughts are being sent to both of you. Please take care. (((HUGS)))

Here's two articles about cats with arthritis: http://vetmedicine.about.com/od/dise...sTreatment.htm and http://voices.yahoo.com/7-home-treat...s-8319665.html.