Bronchitis is an infection of the main airways of the lungs (bronchi), causing them to become irritated and inflamed. The main symptom is a cough, which may bring up yellow-grey mucus (phlegm). Bronchitis may also cause a sore throat and wheezing. Cough. Production of mucus (sputum), which can be clear, white, yellowish-gray or green in color — rarely, it may be streaked with blood. Fatigue. Shortness of breath. Slight fever and chills. Chest discomfort.