Hello, welcome to Justanswer, I will try to assist you with your medical question, and any medical information you seek
Have you had any other tests?
there are a number of possible causes
a lung pathology could be from inflammation, a tumor,a upper airway lesion or irritation,an abnormal connection between an artery and vein, it could be from heart inefficiency as well.
If it is from your upper airway or larynx it could be from similar causes
These are just a few of the possible causes, there are many, many more possibilities, and it would be difficult to narrow down without an exam and tests
If the bleeding continues I think you may need a CT scan or MRI of the chest