I am 39 years and quit smoking 7 years ago. I never coughed, coughed anything up, etc after quitting.  I have always had chronic sinus issues and been on lots of antibiotics and take mucus relief fairly often.  I get shortness of breath out of nowhere.  I have inhalers, and albuterol for nebulizer, prednisone, etc to help, but it takes a while to get back to breathing normal.  I excercise regularly and occasionally get bad headaches from shortness of breath.  Been to doctors and they just tell me my lungs are clear and give me an antibiotic and/or an inhaler.
The inner lining of our sinuses as well as the respiratory tract has lining of small projections called cilia which beat in a definite direction and help in bringing out the dirt and mucus. This is called mucociliary clearance. But the smoking has damaged the ciliated epithelium and hence this clearance is disturbed. Hence, you need to cough out the thick mucus instead of it automatically coming out even after you have quitted. This is also responsible for the sinusitis and the infective agents do not get cleared out from the sinuses. Since the lungs have also been damaged to some degree while you were smoking, you sometimes have respiratory distress or shortness of breath. It will take significant time to recover and will recover only to a near normal stage. You will have to be patient till then. Steam inhalation on regular basis may help.