Do you have any other symptoms aside from the headaches?

Was there any x ray or MRI at time or soon after the injury?
Xray might show if something is easily seen , but MRI will show more layers and cross sections.

What is your treatment plan now?

Have you had any physical therapy? Some will do a comprehensive eval/assessment for the Dr and then discuss the findings.
They usually do some neck traction/compression as well as various tilting to test for symptoms.

It's just good to rule out any other injury that might be needing specific care or treatment.

Soft tissue problems & trigger points can cause a lot of misc pain and even headaches , so if nothing shows as a cause then those should be explored. Or you can read about them and explore that your self easily.

Some TrP info- a tennis ball, dog ball, golf ball etc, or a friends thumb will work great, against a wall or even laying on the floor to help with the pressure on the TrP.
http://www.pressurepointer.com/pain_reference_chart.htm
http://www.pressurepointer.com/Users1.htm