What is the best medicine of dry cough

How Dry cough can be treated ?
It may be du to mild upper respiratory tract infection so you can use home remedies such as herbal Drinks and drink more of lemon Juice to relieve the symptoms , you can also use OTC medication such as Prospan 3 times /day , but if the cough is associated with difficulty of breathing it might be a result of allery so you have to avoid smoking , Pollutants , Perfumes with medication to help you breathe easily such as Ventolin Inhalar 
What Investigations should be done ?
Doctor will as you to do CBC to diagnose viral or bacterial infection , also you may do Chest X-ray 
What are the causes of Cough ?
Post-nasal drip 
Vila Infectio 
Asthma 
Bacterial infection 
Corona 
Advice :
You have to fllow the previously mentioned instructions