Suggest Treatment For Dark Green Mucus While Coughing

I had the seasonal flu during chrismas and on the 1st of January I went to the hospital for dehydration (from vomiting), fever, nasal congestion and sore throat. They did an X-ray and found out I was starting a pneumonia. So the doctor prescribed me some antibiotics (aveenox) for 7 days and he told me it would help me also with my sinusitis. Now it's been 18 days since then and I still have very dark green mucus and postnasal drip but I rarely cough. Is it normal in the process of healing or should I get my sinus checked? Could it be something else?