Hello
You are having sneezing, stuffy nose ( plugged mucus ) , coughing ( over the time sneezing and stuffy nose gone ) .
But sneezing present and recurs with mucus in nose ( this is known as
post nasal discharge ) .
All these symptoms are for the past 3 weeks , may be due to these reasons , these include:
1
Allergic rhinitis , in this there is nasal itching, watery
rhinorrhea,
nasal obstruction, sneezing, post nasal discharge present .
Others are headache , impaired smell ( as you mentioned that taste of mucus is bad ) , morning cough .
Only physical examination find out .
2 Asthmatic allergic bronchitis , all above mentioned symptoms present beside BREATHLESSNESS and wheezing sound .
3 Bronchiectais mild degree .
In my opinion consult a physician and get his opinion as 3 weeks passed and still mucus present.
4
Tuberculosis may be the another such reason.
Hope this will help you.