The most common cause of swollen lymph nodes is infection. Other causes may be inflammatory conditions, abscess or cancer. If your swollen lymph node feels painful, it is probably due to infection. Enlargement that is not very painful is usually derived from a tumor or a cancer. There are some other diseases in which lymph nodes get swollen as a symptom of the disease. These include mononucleosis, rubella, tuberculosis, mumps, tonsillitis, ear infection, mouth sores and sexually transmitted diseases. The way you have described that your lymph node goes back to normal when you are not eating, the most likely cause would be tonsillitis. I, however, suggest you not to base any decision or thought on my opinion and consult a doctor for a better diagnosis.