Thanks for writing to H.C.M. for your query.
I have gone through your query regarding throat infection
with loss of voice and cough
with dark brown sputum.
Considering your complaints and co-relating them with possibilities of pathological process may be going on it appears as you are suffering from acute respirtory tract infection with laryngitis
. this is bacterial infection as sputum is dark brown in colour.
Here few basic investigations are necessary for you like-
(a) X-Ray Chest - P.A. view.
(b) Culture and sensitivity of throat swab.
(c) X-Ray of paranasal sinuses
By these investigations and a thorough examination one can reach to correct diagnosis and that may be plan for treatment.