Welcome for writing to H.C.M.
I read your query for thick post nasal drip
leading to sore throat
to an extent that you feel pain even on yawing and swallowing. You have taken conservative treatment but no response.
Considering your complaints it is clear that your nose and sinuses are responsible or post nasal drip, which in turn give rise to sore throat , therefore your nose & sinuses should be investigated as under-
(1) C.T. scan paranasal sinuses
(2) C /S of throat swab.
(3) FNAC from cervical lymph
A thorough examination is necessary by E.N.T. specialist to extract clues from clinical examination and their co-relation with inferences of investigations to make final diagnosis and than treatment.