Sore tonsils are often a sign of a viral or bacterial infection. If you have a fever, swollen neck glands, or the tonsils are very red or swollen, or have a white or yellow coating on them, see your doctor. The tonsils also can be sore if you have tonsil stones, or have been straining your voice too much. Rarely, sore tonsils can be a sign of cancer or other serious problems.