Suggest Medication For Cough, Runny Nose, And Blocked Nose In A Child

Hello Doctor, my 4.5 years old son has been coughing a lot since 4-5 days. He also has a runny nose and has difficulty in breathing. We give him Otrivin paediatric nasal drops for blocked nose but nothing happens. We also gave him Telekast L syrup still no relief. Could you suggest a better medicine for treating blocked nose, runny nose and for the incessant coughing. His weight is 18.6 kgs.