a good rheumatologist will look at a broad range of evidence - blood work,
x-
rays, possibly an MRI, and most importantly, laying hands and eyes on your sore joints. Whether you're sero-neg or positive, the treatment should be the same.
IMO I don't believe you're being properly diagnosed or treated. Insist on a referral to a rheumatologist; if you're already seeing one, find a better one.
Keep a pain/swelling diary while you're waiting for your appointment.