Community medical question

My knees are become stiffed and painful I am unable to walk and sit on floor comfortably and using chair for namaz and washroom as well ,my knees get swelled but I have got a normal. X ray some doctors consider as the knee effusion and they recomended to aspire it ....I dont understand what to do .....some doctors said that its R A or may be septic arthritis.... Kindly help .. jazakallah