I had apparanetly tested positive for the RA factor 7 years before I ever did treatment my hep C and never knew it. Interferon insulted the heck out of it
and I became extremely symptomatic with severe hot swellling
and redness.
If I were you, I'd seek a consult with a really good rheumatologist to make sure what's going on. It is even possible to have a negative RA factor and still have RA (serum negative RA).