First thing first, you should find out from the doctor what it is, exactly you are dealing with. Alot of times doctors only treat symptoms and do not dig deep enough for the real culprit. Yet, in the meantime I would sleep slightly raised and drink plenty of water, broths and warm glasses of lemon tea from fresh lemons; use honey to sweeten.. Get back to us.
Hi my dad had the same thing but his circumstances are much worse as he has copd, i used to suffer with post nasal drip which makes me feel like i cant cough up any phlem, but im sure its not that, sometimes sputum can be thick and cover your windpipe due to bacteria, all i can say is do not give up with your doctor as my dad had the same and it did cut off his airway and he was in hospital for a week, im not saying that will happen to you, just keep bugging your doc, thats what there there for!! good luck