I would say get another doctor. Call the hospital Doctor directory. If she isn't seeing a rheumatologist, find a good one if you can. Or try an internist, I have been told they are pretty good at finding what's going on.
But please please keep telling her that you love her and care about her, make sure she knows your not going to give up on her. She wants to hear this even if she doesn't feel like it. We like to be reminded that our spouses still love us in spite of our health problems.
Make sure you have a good support team behind you too, someone to talk to and share your feelings with. You need this too.
I have seen how hard these things are on my husband too. He as many husband/wives do, feel helpless and it's important you know what she is going through, and have a positive input for yourself too, so do your homework on her symptoms. And when you find out what is going on with her, read what she is going through and needs. You'll be able to understand it then and can help her If you work at it together, you can make it through anything.
But seek a doctor who you can trust who will walk through this with you to find out the diagnosis.
Blessings to you and your wife
Deb