All kinds of things can go wrong with your tongue to cause sores, but you should have your doctor check them out, since they can sometimes indicate serious health problems.
Sores on the tongue can be caused by allergic reactions, oral herpes simplex virus infection, canker sores, tuberculosis, bacterial infections, early-stage syphilis, allergies, or other immune system disorders.
Most sores on the tongue are caused by ulcers, which normally occur because of too much acidic foods are eaten. Biting the tongue can make sores as well.
Sores on the tongue can be caused by a very large number of things, including cancer. It may also be oral ulceration due to an allergic reaction to a medication.