Since your symptoms haven't improved after taking amoxicillin/clavulanate and an antihistamine-decongestant combination, your cough may be viral or post-infectious, which antibiotics cannot cure. Please stop these medications and consult a doctor for a chest examination to rule out conditions like bronchitis or allergies. For immediate relief, try steam inhalation, drinking warm fluids, and using saline nasal sprays. Your doctor might prescribe a targeted cough suppressant or an inhaler if needed. Please do not worry; a lingering cough after a cold is very common and highly treatable once the exact cause is evaluated by a healthcare professional.