Brief Answer:
Can be due to many causes.

Detailed Answer:
Hello,
Thanks for posting your query.
Low Back Pain Common Causes (considering your age):

• Nerve root syndromes are those that produce symptoms of nerve impingement (a nerve is directly irritated): Herniated discs, Spondylosis and Spinal disc degeneration

• Musculoskeletal pain syndromes that produce low back pain includes myofascial pain syndromes and fibromyalgia.

• Infections of the bones: Bacterial and spinal Tuberculosis

• Noninfectious inflammation of the spine (spondylitis) can cause stiffness and pain in the spine that is particularly worse in the morning

• Renal stone
In the meanwhile, adequate rest, hot compresses, good analgesic medications and avoiding strenuous exercises will benefit you.
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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