should have a predisposing episode of sore throat infection
or any form of streptococcal infection
and associated with fever, multiple joint pains, +/- rashes, +/- palpitation. in your condition u have only joint pain and ASO litre alone positive with RA factor, ESR and CRP normal, so it is very unlikely that it is rheumatic fever.
ASO litre can also be false positive in some other conditions like chronic infection like TB and some liver pathology.
But with your investigations it looks more like a long term inflammatory disease.
more like a seronegative Rheumatoid arthritis
Watch for morning stiffness of joints and small joint pain and swelling.
It is advisable to Consult a rheumatologist
for further investigations and for proper diagnosis and treatment.