Prednisone is a corticosteroid. We people with RA have a love hate relationship with it. It works so fast and so well that we love it. The short term effects of high doses are why we hate it. In high doses, pred can cause increased appitite, irritability and rounding of the face. Long term use can result in adreanal insufficency, bone loss, and cataracts. However, using very low doses greatly reduces the chance of getting the long term side effects.
Being completely pain free (for many of us) and having a ton of extra energy are reasons we love it.
RF (rhuematoid factor) is the test for RA (rhuematoid arthritis). Your test was high but not all that high my was 97 and my rhuemy said that is unremarkable (but, positive). You need to have the tests for inflamation as well though (CRP SED) and probably the one that is more specific to lupus just to rule that out (ANA).
B-12 can actually be low due to an autoimmune disease or due to something seperate so one does not rule out the other.