Suggest Treatment For Child Suffering From Constant Cough

My 7 year old daughter is having cough from over last 3 months. I have shown her to many doctors who said her chest is clear and maybe she s allergic to something and prescribed different cough syrups and allergic medications. Still there s no change in her cough. Although in her blood report esinophils are in normal range, her latest doctor has told to take singulair and instaryl and allegra. Still from last three days there is no change in her cough pattern. Now when she s was two year old a doctor has told that she s having asthma and prescribed ventornil and montek lc kid... so I have today started giving her ventornil. .. i don t know what to do to relieve her from cough. .. i ve tried all home remedies too