Although your description does not define the extent of discoloration on your teeth, I would like to suggest one thing straight and simple--- there is no medication which can whiten your teeth. Daily plaque removal by efficient toothbrushing will be the most important effort to make sure that the situation doesn't deteriorate further. If you actually want whitening of teeth you will require bleaching which will be done by the dentist using good quality materials. You should visit a dentist as soon as possible to get your condition evaluated so that the right treatment options can be explained to you. Regards.