Coughing up smelly, yellow mucus for 3 weeks?

I've had a horrible, nagging cough that began about three weeks ago. I began coughing up yellow mucus shortly after, which typically gets stuck at the back of my throat. I went to the doctor twice who suspected bronchitis and prescribed me an antibiotic. Unfortunately, the medication has not helped. It's been a week since and the mucus is now causing a horrible taste at the back of my throat and producing a foul smell. Is the bronchitis progressing or is this still merely bronchitis? Nothing is helping! Coughing is the only main symptom. I've had a decrease in appetite and I've been a little more fatigued than usual, but no high fevers or anything.