How did I land up with this cough?

The cough that has lasted quite a few days in your case and does not get better on its own may be bronchitis and it can be caused due to a number of reasons:

Viruses: : Several viruses have been known to cause bronchitis and some of the common ones include - Influenza A and B virus; these are also referred to as the flu in common language. They are generally responsible for acute bronchitis.

Bacteria: Certain bacteria such as 'Mycoplasma pneumoniae' can also lead to bronchitis, especially of the acute form.

Inhaling irritant fumes, chemical solvents, dust, etc. over a period of time can lead to chronic cases bronchitis though a sudden exposure can also precipitate an acute attack.

Smoking is one of the major causes for developing chronic bronchitis.

People with a weakened immune system are at increased risk of developing bronchitis.

It must be noted people with chronic bronchitis go through periods when their condition becomes worse than general. During such times, they may develop acute bronchitis (caused by viruses or bacteria).