Pain, swelling in lymph node behind neck, area bruised, stiff. Hypothyroidism. Energy drained out. Any medication?

HI. On Monday one of my lymph nodes on the left back of my neck at the base of my skull started swelling and becoming painful. It s now been 4 days and I have a cluster of swollen lymph nodes at the base of my skull going down to my shoulder. The area feels bruised and stiff and I get shooting pain down my shoulder and on the front of my neck down to my clavicle . I don t have a cold, no animal or insect bites either. I do have hypothyroidism and when I try to feel the lymph nodes on the front of my neck the left side feels swollen but the right side feels like it has a little lump. I have been taking Advil for the pain and Benadryl at night. I feel drained of energy. Any recommendations? I ve been looking online and it sounds like it should go away in a week or two.