Brief Answer:
Likely to be muscular sprain.

Detailed Answer:
Hello,
Thanks for posting your query.
Common causes of midback pain radiating to the side are-
Poor postural habits
Muscular strain
Ligaments sprain
Herniated disc
Spinal stenosis
Osteoporosis
Fibromyalgia
The first step is to ensure that you maintain an appropriate posture while working on the computer. Take frequent stretch breaks and drink lots of water. Discontinue using pillow while sleeping straight. Do not lift heavy objects, especially after bending down. Eat a healthy wholesome meal which should satisfy your minerals and proteins requirement.

The most essential and long lasting remedy is exercises. There are certain back strengthening isometric exercises that you must learn from a physiotherapist and perform them at home or work whenever possible.
Last but not least, if its unbearable take medications or muscle relaxant prescribed by your physician. And if it has been long standing illness visit your orthopaedician and clinically-radiologically establish a diagnosis to commence definitive treatment.

I hope this answers your query.
In case you have additional questions or doubts, you can forward them to me, and I shall be glad to help you out.
Wishing you good health.
Regards.
Dr. Praveen Tayal.
For future query, you can directly approach me through my profile URL http://bit.ly/Dr-Praveen-Tayal

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