I keep coughing up mucus but I feel fine??

So Sunday I had a sore throat and was losing my voice. I took Mucinex and Tylenol and I was also coughing up mucus. In the morning it's yellow/green but during the day it's foamy white. I went to the doctor and she listened to my lungs and looked at my throat and said I have an upper respiratory infection. I went on Tuesday to the doctor and my voice is mostly back. I've been taking my temp and it's normal 98.4. I have no other symptoms. I'm eating fine etc. But every morning I wake up, I keep coughing up green yellow mucus. This is gross but I blew my nose and noticed the color of some of my snot was the same as the stuff I coughed up. Is there a chance this is post nasal drip from sleeping? I coughed up mucus today with a chunk in it. I always wake up with a sore throat that slowly gets better. I'm worried I have pneumonia but surely she would've heard something when listening to my lungs and my voice wouldn't be getting slowly better.