Viral throat infections and colds usually can cause lymph nodes in the neck to double in size. A slight enlargement means that the lymph node is fighting against the infection. You've given your son an antibiotic and anti-allergic therapy, which is correct medical procedure. After the infection is gone, the nodes will slowly return to normal size after two to four weeks. However, it is best to verify treatment with a licensed medical professional before administering any treatment. You might want to consult a primary health physician to be sure that infection is, indeed, the cause of the symptoms he reports.