Tenderness behind the ear can be a spasming muscle that connects to your upper neck. It can also be the cause of head aches. The C-1 (atlas) to occiput (base of skull) joint can be injured. There are also tendon anchoring points that can pull out and form a bone spur.

A physiatrist (Physical Medicine and Rehabilitation) may be helpful or a Physical Therapist, too.

My best to you.