I've been taking Cheratussin AC 10 mg-100 mg/5 mL Oral Liquid since this past Wend, and so far it hasn't worked .. how long dose it take for it to start working? the doc said my cough was internal cough, and theres nothing he could do. but why would he give me that med if it wouldn't do anything? can someone please help?? ... i don't know if i should go back to the doc or just wait and see it it goes away on it's own/