Hello, complete course of RNTCP regimen cures tuberculosis , negative sputum ,blood culture and pus culture confirms diagnosis . You might have lost weight ,its common with TB,have one egg daily, have meals at regular intervals, don't skip meals , have meat ,ghee, egg, fish etc... do exercise daily ,sleep well ,avoid worries .One should not have any blood borne diseases in the past to donate blood,I don't think they accept your blood ,moreover your weak