Blood-streaked sputum for over 2 weeks without other symptoms

I have been having small amount of blood-streaked sputum for over two weeks now, without any other symptoms such as coughing, chest pain, temperature or fatigue.  The blood is not frothy or pink. It looks mostly fresh in the PM but a bit of rusty in the morning. Chest CT only shows historidcally healed and currently inactive TB which I may have contracted before without self-awareness. I took antibiotics for 10 days, but small amount of blood-streaked sputum continues, more in the PM than AM (there is no or little less fresh blood in my sputum now immeidately after getting up in the morning, but getting more during the day). I am not a smoker.  Doctor's preliminary check of my nose or throat showed nothing as possible source of bleeding.  It's really puzzling, irritating and concerning.  Please help!