Since your cough has lasted for two weeks without improvement despite taking Cofdex, please stop self-medicating and consult a doctor. A persistent cough can be caused by underlying issues like a respiratory infection, asthma, allergies, or acid reflux, which over-the-counter syrups cannot cure. A physician needs to examine your chest to determine the exact cause and prescribe targeted treatment, such as antibiotics, inhalers, or stronger prescription medications. Continuing OTC cough syrups without a diagnosis is not recommended.