A cold and cough lasting 20 days may be due to a prolonged viral infection, sinusitis, allergy, or sometimes a secondary bacterial infection, so it?s best not to ignore it. Drink plenty of warm fluids, take steam inhalation, and use simple medicines like Paracetamol for fever/body aches or Cetirizine for allergy symptoms if needed. If you have thick phlegm, chest pain, breathlessness, high fever, or no improvement, consult a doctor for proper evaluation and possible antibiotics or tests.