If there is tenderness on pressing the neck from outside, then this could be due to spinal nerve compression, inflamed sternocleidomastoid muscle as in TMJ (this would respond to physiotherapy, pain killers and cold compress), swollen lymph nodes if you can feel a mass, an abscess
if you can feel a mass, a clot in
the carotid artery or due to a muscle pull.
Please consult your doctor regarding this. Take care!