Hi! I Am Having Excessive Sputum/mucus Problem From Last Two

Hi!
I am having excessive sputum/mucus problem from last two months. With a feeling of fever and dizziness. Doctors didn't find any symptom of bacterial infection or throat problem but I am coughing up excessive sputum and now discovered small blisters on the crease of my tongue. The doctor asked my to use benadril and neurophin but it doesn't work.can you please tell me the reason of such an excessive sputum as this never happened before.
Thanks