Hi, My So Is 7yrs 9 Months. He Is Always

hi, my so is 7yrs 9 months. He is always suffering from cough(allergic and dry) mostly when he is sleeping. because of this cough, he is not able to sleep properly and vomits out in night. My pediatrics says that he is allergic. he has started singular for the allergy for three months but seems not effective enough. Again is has this problem Now he is taking Grillintus BM thrice a day.Omanacortil twice a day for 3 days.but he is having server cough. Please suggest.