I would say you have a sinus infection. And you could possibly be having the start of bronchitis in your chest.
This yrs flu is going straight to the bronchials, really no fever to speak of, coughing starts out minimal but as the drainage continues especially at nite it drains into the lungs or chest area, with minimal fever still. Watch the cough as I said this crap turns into bronchitis almost over nite. Watch to see if chest hurts when inhaling, if so get to urgent care or emergency for antibiotics
Good luck and be well
Deb