Pain in the left side of the neck is considered to be caused by inflammation of the lymph nodes. Since there are very many lymph nodes in the neck, when the lymph nodes are infected by bacteria, it can lead to lymph node pain, redness, swelling and other manifestations. The common causative bacteria, Staphylococcus aureus or Streptococcus haemolyticus, need to be treated with oral antibiotics, such as cefixime and levofloxacin hydrochloride. The symptoms of lymph node inflammation can be controlled after about a week of treatment. If there is pain in the thyroid gland, that is, if there is enlargement in the front of the neck on the lower side, near the sternum, consider a thyroid lesion. Commonly, thyroid adenomas or nodular goiters are cystic in nature, or they may be intracapsular bleeding manifesting as thyroid pain, and there may be a sudden increase in the size of the thyroid mass, which needs to be checked at the hospital. Consider thyroid disease caused by a subtotal thyroidectomy.