After going through histiry It seems you have a upper respiratory infection
,mostly it is a viral infection but you have cough
for >15 days it is possible to have secondary bacterial infection as there is mucus and sputum. Pain on swallowing is because of Congestion of Throat and Inflamation.Also nasal passages are blocks. You have to see ENT surgeon . In the mean time Gargle wit hot water with salt
( Saline Gargle) take some analgesic
,which will help you.Even OTC Nasal decogestant may be used. after you consult a course of proper antibiotics and other drugs will cure you follow any investigation suggested by ENT Surgeon.