“Straightening of the cervical spine” is not a diagnosis. This may not even be a disorder as many patients hold their neck “straight” on X-ray without any symptoms. Neck pain originates from discs and facets. If the MRI notes no evidence of disc degeneration, then the problem most likely will be in the facets.
Facet disorders typically do not show up well on MRI as the injury is “smaller” than the resolution of the MRI scanner. Headaches quite commonly are generated by the C2-3 and C3-4 facets. You might try a chiropractor initially for treatment. If that is not successful, see a pain injection specialist for diagnosis and possible treatment of this disorder.