Hi, Coughing for more than 3 weeks indicating towards lower respiratory tract infection either due to bacterial infection like tuberculosis, pneumonia/ fungal infection. these infections may lead to pleurisy or pleural effusion causing chest pain on deep breathing. Go for chest x ray PA view, sputum examination, total blood count, tuberculin test, CT scan of chest,. Consult a physician for physical examination and treatment. I think you need either anti tubercular treatment/ specific antibiotic/ antifungal treatment against causative organism. Thank you for consulting HCM.