Flexiril is absolutely positively the wrong medication. Wrong track, wrong railroad, wrong track gauge.
A muscle relaxant is the last thing you want in your system. It degrades muscle tone and is guaranteed to cause you chronic pain and paralysis. And you don't want a cervical collar either.
An x-ray is also positively useless. An MRI is helpful, but not necessary. The problem can be diagnosed from the pain dermatome.
A problem with chiropractors is that they do not have access to an MRI, among other things, and in many states have limited prescription rights.
You need an anti-inflamatory, prednisone, followed up by ibuprufin, mild intermittant axial traction and range of motion exercises.
Have you seen a chiropractor? It's an easy fix and may only take a few office visits.