welcome in H.C.M. for consultation.
I read your query regarding cough with scanty sputum and some times with blood .
As you said that your X-ray chest is normal, and you notice blood when you were clearing your throat. You are also having headache and you were using nasonex
for your post nasal drip
Considering all these aspect of your complaints, I suspect that you are basically having sinusitis
and this in turn giving rise to post nasal drip which is creating soreness in throat and thus dry cough
with scanty sputum is experienced by you. Blood in phlegm is most likely came from sinus.
You are advice for these basic investigations-
(1) C.T.scan of paranasal sinuses
(2) Sputum for culture and sensitivity
(3) Sputum for --Afb.
I hope these investigations will disclose the disease which can be than managed.