Hi and thanks for your questions,
what you are describing is classical polyarthitis. This could mist of the time be of rhumatologic origin.
Autoimmune diseases like rhumatoid arthritis, systemic lupus erythematosus
are generally implicated. Conditions like polymyalgia rheumatica
must also be excluded.
Laboratory exams including the rhumatoid factor, erythrocyte sedimentation rate
, C reactive protein, Anti Nuclear Antibody
measure, cANCA and pANCA are usually of diagnostic importance. X rays at times could be important too.
Consult a rhumatologist for a comprehensive and appropriate care.
Thanks and best regards,