Why Am I Still Clearing My Throat With A Dust-like Feeling And Mucus Weeks After A Sinus And Upper Respiratory Infection, Especially Worse At Night?

A few weeks back I had to go to the clinic because I Thought I had The Flu, but tested negative for the flu and covid. After examination the Doctor said that I had a upper respiratory infection and sinus infection. For a week or so now I have been feeling like I have dust in my throat and mucus which makes me constantly clear my throat .........It seems to get worse at night