Is there a reason why i am still coughing up mucus when i'm not sick anymore?

Persisting cough: Even after the acute phase of an upper respiratory infection when you are no longer contagious, the membranes and glands lining the nose and windpipe can remain somewhat inflamed. Inflammatory cells in these membranes produce chemicals called secretogogues that continue to stimulate mucus-producing cells. This inflammation and excess mucus production can persist for days to weeks.

Yes: Assuming you don't smoke, your cough may be from a post-viral cough , asthma, or even a sinus infection. EVen though the active infection may be over, bronchial irritation may linger for weeks.