Dear, thanks for the question. Sore throat is caused by viral/bacterial infections of upper respiratory tract. Sore throat generally starts with viral which is followed by secondary bacterial infection. Soft swelling behind ear is probably swollen Lymph Node (a glandular structure containing antibodies). Lymph nodes enlarge in response to infection in neighbouring areas from where blood goes through the lymph node. This enlargement of lymph nodes is reactionary in nature. This lymph node enlargement is generally non serious. However if doesn t subside after treatment of sore throat with a course of antibiotics, then you need to consult a doctor to rule out Tuberculosis or any other serious disease. Wish you a healthy living ahead.