Your current medication, amoxicillin, is an antibiotic. Since you see no improvement after five days, your cough might be caused by a viral infection (like bronchitis) or another issue that antibiotics cannot treat. The chest pain is likely muscle strain from severe coughing, but it is important to rule out other conditions. Please do not start any new medication on your own. I strongly recommend visiting a doctor for a physical examination and potentially a chest X-ray. They can prescribe the correct treatment, such as targeted cough suppressants or inhalers. For now, rest and stay well-hydrated.