Thanks for writing your query to us.
History of longstanding fever
of 1 month duration, cough, significant weight loss
along with chest Xray showing pleural effusion
as you had mentioned most likely diagnosis is Tuberculosis
. Since you had also mentioned that pleural fluid examination done twice is negative for tuberculosis which is unlikely for tuberculosis.
Error in pleural fluid examination can be the cause. Try to get pleural fluid examined from a reliable pathology lab. Pleural fluid ADA(Adenosine
deaminase Test) is specific for tuberculosis. If that is negative that diagnosis needs to reevaluated. Tuberculosis takes time to respond to the antituberculosis drugs, so kindly continue the medicines & do not stop the medicines without consulting your treating doctor.
Wish you good health.