What is the best medicine for 2 days of productive cough ?

See a doctor: This could be anything from bronchitis, a viral pneumonia, or a bacterial pneumonia, or any other pulmonary process; there are also many questions to be asked, such as presence of fever, pain with breathing, other symptoms. It is impossible to determine with this limited information. See a doctor for evaluation.

Fluids: Keep drinking fluids, use Guaifenesin (mucinex). You should visit your doctor to see if you need antibiotic, bronchodilators or some other treatment.