Coughs lasting about a month have a variety of different causes. One such cause is a prolonged infection or repeated infections. This could be with the more common viral upper respiratory infection, especially if you have been exposed to other sick contacts. Another prolonged infection to consider is pertussis, or whooping cough, which is a bacterial illness
that is starting to affect more of the adult population as vaccination rates have dropped off in recent years. Your doctor
can test you for this , but unfortunately treatment doesn't help this far into the illness (typically the cough in this case is resolved by 2 months). Another common cause of prolonged cause is upper airway cough syndrome, also known as post-nasal drip.
In this scenario, often caused by allergies or sinusitis, you may feel like there is irritation of the back of the throat due to mucus coming down from the nose. Decongestants and nasal steroids can often bring relief if this is the cause.
Other causes to consider are asthma or other lung disorder, gastroesophageal reflux disease (which can present only with cough), or the side effects of any medications (such as ACE inhibitors). You should see your primary care physician
to discuss these issues. He or she may choose to do a chest x-ray if your cough continues to persist.