Hello Good Evening Doctor.. I Have Cough For So Long

Hello good evening doctor.. I have cough for so long many weeks sometimes I taka med. But it does not work then I saw carbosistine rhinatanol I have plengm also doc. It's 125ml rhinatanol in 27 years old I'm afraid to take med.if I don't know the brand.. For me I read 15ml syrup to take it that high dosage doctor for me? Thanks..