Blood in sputum with fever every evening

My father, Age 66, is having blood in his sputum with fever in evening from 3 months. following tests have been conducted: Sputum Test - Negative, TB not detected CBNAAT - Negative CT Scan - F/S/O - Right lower postero-lateral lung abscess with perilesional ground glass opacity and few enlarged node. patchy ground glass opacity in right perihilar and lower lung. Cytology - Negative for carcinova. No malign cells detected. Fungal Infection - Negative Ultrasound abd - Normal, no abdomen infection, no lymphnodic structures detected Before conducting the CBNAAT test, medicine for TB was given for 1 month. However there wasn't any sign of improvement, so after CBNAAT test this medication was stopped. From above tests doctors have ruled out Cancer, TB, andfungal infection. However the root cause is still known