Hi
Welcome to HealthcareMagic forum
This problem of yours could be due to
Chronic pharyngitis. There are various causes which can lead to this condition such as
acid reflux disease,
chronic sinusitis, infection of the tonsils,
allergy, etc. You need to get it evaluated by your doctor. Secondly, the blackish sputum could be due to the sinus secretions coming behind the throat.
Wish you good health
Regards