Since your current medication isn't helping, the right alternative depends on your cough type. For a dry, hacking cough, a suppressant like diphenhydramine can help quiet the cough reflex. If you are coughing up mucus, an expectorant like guaifenesin will help thin and clear the phlegm. Staying well-hydrated with warm fluids is also highly beneficial. Since your cough is severe and has lasted three days, I recommend consulting a doctor for a proper chest examination. This ensures you receive the correct treatment and rules out underlying conditions like bronchitis, especially if you develop a fever or shortness of breath.