Chronic whiplash injury is not well understood at this time. Most doctors agree that at least six months of conservative care is needed before trying something else. Surgery is one option. A neurosurgeon can at least evaluate you and let you know what might work.
A recent study found that some patients have atypical motion after whiplash. This is defined by less than 10 degrees of motion in each of six neck motions. Adding up all degrees of motion for the six directions would be less than 60 degrees. The patients in this study with less than 60 degrees total motion had some differences in personality that could explain their results.
If you fall into this group, behavioral therapy may work best. Try to find a behavioral counselor who has training in chronic pain after injury or accident.