Cold and Cough

Patient: I’ve been coughing since Friday and my chest hurts and it’sdifficult to breathe a little. I went to the doctor yesterdayand he checked my chest and said it was just a cold.I do have post nasal drip and my head is hurting. He told meto start Mucinex DM. I did yesterday all day and it helped withthe coughing but I took it today and I am still coughing and mychest is hurting. He gave me Z pack to hold onto if I am notbetter by Wednesday. How long does Mucinex take to work? Shouldit already be working by now? And if I take the Z pack will ithelp?