When i am putting a pressure on left side of my back i feel some pain so is it just muscle spasm or my kidney ?

Depends: Kidney pain usually present with localized tenderness at the bilateral flank regions, which may radiate to the lumbosacral spine and inguinal area. The pain usually presents as dull, achy, constant, cramping pain, with intermittent sharp stabbing pain .However, musculoskeletal pain due to muscle spasm usually presents with dull spasm to sharp pain reproducible with palpation, and position changes

Various causes...: Your symptoms could arise from various possible causes, including myofascial pain, muscle spasms, a (left) kidney problem, discogenic pain, spinal joint (facet or SI) inflammation, and other possibilities. See your doctor for specific diagnosis and treatment. If you have a fever, progressive weakness, bowel or bladder problems, or your pain does not improve see your doctor as soon as possible.