Newly diagnosed, but I think its a wrong diagnosis?

I have just recently been diagnosed with fibromyalgia from a rheumatologist. The only pain I have is in my SI joint that has been on and off now for several years. The SI pain is mostly at night and I feel better after stretching in the morning. My SI joint feels stiff and painful if I sit too long. This SI pain has now been pretty constant for the last 8 months. I am now suffering some numbness in my hands on and off. That is causing some nerve pain in my shoulders, elbows and wrists. I have also had arm weakness. Other then these symptoms I do not have any other complaints. No muscle pain, no headaches, no depression or anxiety, no fog, slight fatigue but I think that is from the pain waking me up and night and not getting a good night sleep. I have had the whole gamete of tests, blood, xray, mri, and everything seems okay. I just feel like this diagnosis doesn't really fit but I don't know where to go from here or if maybe I am in denial? Any input is greatly appreciated.
Thank you,
Traci

Have you had an appointment with a neurologist to check for spinal issues?

There is a condition where you can have arthritis in the SI joint.

Thank you all for the input. My doctor was originally convinced that it was ankylosing spondolitis saying I was a textbook case but my lab was negative for the gene, xray looked good and MRI did not show inflammation. I am going to get a second opinion and this input has pushed me to realize a second opinion is most likely a good idea. Thank you all for your help and if this is the correct diagnosis I will be back to chat with everyone.
Thank you,
Traci