I would treat for whiplash, sore neck muscles , trigger points and see if those things help.. Much of that you can do as self care via a web search & you tube for info..
Try heat/Ice on the muscles of upper back & neck which ever seems to work best.

Trigger points in muscles can cause headaches..
Free Trigger Point Charts
Pain Reference Chart

A thumb or any small ball or even a tennis ball on floor will usually work to try it your self. Be aware of and avoid artery & veins..