Talk to Endocrinologist on Swelling Between Neck And Shoulder

My mother is 42 years old. Her neck has been swelling up like a balloon for a year. Initially, it used to swell once a month, but for almost the last 6 months, it swells every 10 to 15 days and subsides on its own after 3 days. Sometimes it happens after lifting weights, sometimes it is linked to her menstrual periods, and sometimes it happens without any reason at all. There is no specific timing for this. Because of this, she feels pressure on her shoulders. The general physician could not diagnose it. Kindly tell me what could be the reason for this?"