I've had a cold for four months, what could be causing it?

I've had a cold for more than four months. It started with a runny nose, and then a couple of weeks later I started coughing. I do sometimes cough during the day, but it mainly occurs when I lie down at night, and first thing in the morning. I'm otherwise well, have no chest pain and when I'm not coughing, I can breathe normally. I know colds are caused by viruses, so antibiotics don't help, but is there anything else I could try?

- Dr Rosemary Leonard

You are right that nearly all colds, which cause a runny blocked nose, together with a mild fever, sore throat and sometimes a dry cough, are caused by viral infections. This means that antibiotics are of no benefit, and the symptoms should clear up in a week to 10 days.