Back pain is common in 80% of adults, and people usually think of back pain as being all over the back, but back pain can be one-sided only and can be a very annoying thing,
One of the situations in which you can worry about back pain is one-sided

Age: Older adults may have a minor injury that leads to a more serious condition – either due to their low bone density or arthritis that causes pain.

Sports: Athletes may experience more musculoskeletal wear than the general population, and are often more prone to fractures, herniated discs, or arthritis.

Tissue-related back pain is more common

Unilateral spontaneous back pain can occur for a variety of reasons, but is usually associated with soft tissues (muscles, ligaments, joint).

The back muscles extend up and down the left side and right side – they don’t cross the midline (spine), so if you’re irritating a muscle on the left side of your back, you’ll likely only feel pain in that area.

Dr. D’Emico said: ‘Someone with tissue-related pain will feel severe pain. Oftentimes, the area is tender to the touch and restricted range of motion due to the discomfort and pain you feel.

Causes of tissue-related discomfort include:

Deep sleep: If you have been sleeping for a long time on one side of your body, you may find that the muscles on only one side of your back are tense, causing pain.

Sitting at the computer: If you are at work and sitting for long hours at the computer, you may end up feeling pain on only one side of your back.

Travel: Being stuck in a sitting position for a long time can cause muscle tightness, so take frequent breaks if you’re traveling by car or get around on an airplane whenever possible.

Usually, muscle-related pain will subside if you use anti-inflammatories and rest with ice.

Back pain related to the left or right organs
If the pain you’re experiencing is a little deeper in the back, and you also have other symptoms, it may be related to an internal organ. See your doctor, as these are signs of infection or irritation:

Intestines: Colitis may affect one side of your lower back, but you are also likely to experience abdominal cramps, digestive problems, and weight changes.

Kidney: Infection or a kidney stone may also cause one-sided back pain that occurs between the bottom of the rib cage and the hips. Again, you can expect other symptoms such as blood in the urine, pain when urinating, or a fever.

Uterus: Pain on the right side of the lower back may be due to fibroids or endometriosis. Along with the pain, you will likely also have problems with your period, and a frequent need to urinate.