I Am TrYing To Treat My Cough With Cough Syrup.

I am trYing to treat my cough with cough syrup. I had finished 1 bottle of the robitùssin cough suppressant My coughing greatly reduced, but I still cough once in a while. I bought again another bottle but this time it a cough and chest congestion DM. I am hesitant to take because I just finished the other bottle last week. Should I still take it. Please advise. Thanks.