Brief Answer:
Detailed clinical examination and investigations and treatment

Detailed Answer:

Hi,

Noted the history and understood the concerns.
Since the back pain as explained is going on for a few months without any relief by the medications as you have mentioned the obvious cause has to be found out for a specific treatment.
Rest seems to help but no permanent relief.
The pain is on one side that is right side, middle back.
The most probable cause can be muscle spasm with repeated stress not allowing to heal and become painless.
One sided pain can be due to osteoarthritis of the inter-vertebral joints.

Hence this can be well diagnosed by the following:
Clinical evaluation, examination by a Doctor, preferably an Orthopedic Surgeon.
Supportive MRI of the affected area helps the most for getting an internal problems if any.
Once the proper diagnosis is made, the treatment can be specific and of help/cure.

Till then take a full rest in the most comfortable position.
Continue Flexeril as this is a muscle relaxer; Advil or Aleve which ever suits you the most as anti-inflammatory and painkiller.
Apply rubefacient local liniment that gives local warmth and thus helps to relieve pain and spasm.
Ask someone in family to have local examination for any swelling, redness, mass, hardness or so on and please let me know.

Take care.
With Regards.

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