Talk to Pediatrician on Chest Congestion

Its been about 20 days when my son got flu, nose was running and having fever, then fever got worse like 102 to 103 , rushed to a doc he suggested an antibiotic and antielergy and couoh syrup. There was no improvement i have changed the doc after 5 days of this medicine, new doc just changed the medicine and suggested aezomx once a day for 5 days, anfter 2nd day fever got controlled and cheild stared feeling better. Now i have completed this medicine also . Rest everything is fine , but still his swear chest congestion. Everytime he cuugh there is this sound of khasss khassss… please suggest.