Colds and influenza are caused by viruses. In three or four days your body will make enough antibodies to kill the virus. However, the virus may have irritated the lining of the breathing passages and this may cause a cough. A cough is not a bad thing: it is there for a reason. It helps defends your lungs by making sure that any secretions your tubes produce are coughed up rather than settling in the lower lungs where they would cause trouble. Similarly “phlegm” or “sputum” is there to act as a barrier to catch the dust and germs that we breathe in.
Assuming you are otherwise feeling well, you need not worry if your cough and phlegm takes two or three weeks to settle, especially if you are getting gradually better. Coughs may be worse at night because you are breathing in cold, dry air which irritates the breathing passages. Smoking or inhaling other people’s smoke makes coughs worse.
Your doctors will not prescribe antibiotics for coughs, colds and flu-like illnesses because they do not work against viruses. Antibiotics can cause side-effects. Some bacteria develop resistance to the antibiotic which can prevent it helping when it is really needed. Coughing prevents mucus from blocking the air passages. It can be dangerous to try to stop this with cough mixture.