Hello, the information you have provided is not enough to pin point the cause of back pain. So consult a PT. To manage your pain apply hot pack, start with mild back stretches, try not sit more than 30 min in one position, take 2+ min walks after every 30 min or so if you have a desk job. Increase your your physical activity.
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This might be helpful http://physiofitplus.weebly.com/blog/why-we-suffer-form-muscular-back-pain