Help solve the mystery!

My cat Mama is having some problems that have both the vet and me completely confused and frustrated. For the past couple of weeks she has had problems walking. The first time this happened she stopped walking, her lymph nodes in her rear legs got swollen, layed on the bed all day, and her fever went over 104. We ran blood tests and everything was within normal range. So we started her on antibiotics and within a 36 hours she was walking like normal. I kept her on antibiotics for about 7 days and as soon as we stopped the antibiotics, she started lossing the ability to walk again. This time she didn't get a fever, but her lymp nodes were still swollen. I started another round of antibiotics but this time did a full 10 day course. Then, about 2 days later she started having trouble walking again! The vet thinks that it might be an injury in her leg, like an injured ACL but that doesn't explain why her lymph nodes are swelling. He said that he could remove the lymph nodes and see if that could be the problem, but she has a severe heart murmur so that would be a high-risk procedure. Any suggestions would be helpful!

You've got me. Could it possibly be an autoimmune problem? Like people with Lupus will sometimes have lymph node swelling. Could she have arthritis?
How old is she? Do you know if she has gotten into something that she should not have?

I would certainly get a second opinion I think. Have you considered contacting the major Vet training school in your state, many have and mine does have a clinic that you can bring your pets to. It is a teaching clinic and the Vets that train the Vets are there in person and supervising, so it might be worth a try. I know in my state you almost always have to get your Vet to refer you to the clinic, but unsure how other schools in other states would handle it.

She's a little over 2 years old. It's a surprise that she's made it to this age. The vet said that he doesn't see cats with arthritis very often, and very very rarely as young as she is. An autoimmune disease is possible, do you know of any that are found in cats? Since this has happened 3 times, I don't think it's likely that she got into anything to cause this kind of reaction.

I just moved a few months ago so I don't know of any vet schools around here. I think we're going to try x-rays next and if that doesn't show anything, then I'll look into getting a second opinion. As of yet, medically it doesn't seem if anything should be wrong with her so a second opinion might not do any good until I exhaust my options with my current vet.

Thanks for the replies so far!

Where are you in Texas? Texas A&M has an outstanding vet school. So does Oklahoma State, if you are in the panhandle.

Dallas has some outstanding Vet groups that require a referral from your local vet.

I'm in the San Antonio area. I'm not sure where A&M is but Dallas is 6 hours away and Oklahoma is even further. I'd rather try my other options before making a long trip. Mama HATES car rides and every time I take her somewhere I worry that her heart's going to act up. It's always a catch 22 with my cats!