What Causes Prolonged Vomiting, Cough And Fever In A Child?

My 2 and half year old niece is suffering from vomiting, cough and fever for last 15- 20 days. She lives in Varanasi. Had shown her to 2-3 doctors in Varanasi but unable to get satisfactory results. She was fine for 4-5 days after treatment, but again problem started for last 2-3 days. Can you suggest a good pediatrician in Varanasi pls?