A 20 year old male presented with complaints of Low backache with occassional swelling in both lower limbs.Also gives history of pain in joints esp knee & shoulder.X ray LS spine & hip are normal.His Hemoglobin is 10 gm%.ESR is 90 mm/1st hour.All other investigations ( ( RBS,Chest X Ray) are WNL. 1.What could be possible diagnosis?

2.What more investigations are needed?