HI i have gone through your mail and as you said that you are residing in a polluted city and you are teacher and remain in contact with chock dust,these are the social factors responsible for developing sinusitis
,as you lie down you feel dripping of mucus in throat from nose this is post nasal drip
,this post nasal drip extends infections from nose and sinuses to throat thus developing sore throat
.this clinical condition is called as upper respiratory tract
infection,to manage this you should go for these basic investigations like-(1) X-ray paranasal sinuses
,(2) culture and sensitivity of throat swab,(3) blood-CBC,ESR,blood sugar etc.As for as management is concern you should contact your E.N.T.specialist for your clinical examination of your nose and throat,after this diagnosis is made by clinical co-relation of clinical findings with inferences of investigations,in this way after establishing the diagnosis one can plan for treatment.Thanks.