Congratulations on getting a lot of good results back on your blood tests!
One of my doctors told me that beta-2 microglobulin was prognostic but not diagnostic. In other words, it really isn't specific enough to indicate myeloma on its own, but it does contribute to the broader picture of what's going on. There are many conditions that can increase that number, including (I believe) certain kidney issues. This wasn't a huge jump.
I know it's hard, but try to look at the numbers as a complete picture. That's why this disease can take so long to diagnose and classify. If one number told the whole story, sorting out all the labs would be much less frustrating.

Hang in there!
-W