Cetirizine is a 24-hour antihistamine, meaning its effects naturally wear off and it must be taken daily for ongoing relief. If your symptoms are due to allergies, a daily steroid nasal spray (like fluticasone) provides much better, lasting control than pills. However, if you have a viral common cold, it typically resolves on its own within 7 to 10 days. In this case, supportive care like warm fluids and saline nasal sprays will help ease symptoms. I highly recommend consulting a healthcare provider to determine whether your symptoms are allergic or viral so they can prescribe the most effective treatment.