Pain that persists beyond the expected time for healing is called chronic pain. In the case of a whiplash injury, most of the physiologic healing of the soft tissues takes place in the first eight to 10 weeks after the accident.
This is not to say that chronic pain can't be treated or won't respond to treatment. Many whiplash patients can and do improve with a rehab program. A physical therapist works with the patients to restore full and normal, pain free motion.
Weakness of the muscles around the neck may be part of the problem. A strengthening program may be needed. And because tiny receptors in the joints can be damaged during the injury, treatment to increase or restore proprioception can be very important. Proprioception is the joint's sense of position in the spine during rest and during motion.
Some patients seek out the services of a massage therapist, chiropractor, or acupuncturist for painful symptoms of chronic whiplash syndrome. If your physician has ruled out more serious problems such as tumor, infection, or fracture, then you may want to pursue various other approaches to treatment mentioned.