Hmmmm Interesting!!!! When you say tests for RA, are you talking about ANA and Rheumatoid Factor (RF)? Juvenile rheumatoid arthritis (JRA) is not uncommonly seronegative (negative rheumatoid factor). In fact, positive RF in cases of JRA is a marker of bad prognosis. So a negative RF does not rule out RA if the clinical probability is high. Of course I am in no position to make any diagnosis from here but just thought I would let you know this.
By the way, there are 2 different things: Arthralgias, which are pain in the joints, and arthritis, which is inflammation of the joints (pain, swelling, redness, warmth). Just a medical pearl for the day.
EDIT: I just read your post again... What do you mean by arthritis in the chest? Costochondritis? We don't need to keep talking about this here on Jen's thread LOL You can PM me.