Severe pain on my left side on my back. hurts to breathe or move. sometimes takes my breath away bc it is so painful. what could it be ?

Muscle spasm: Likely muscle spasms. Depend on what part of the back. Could be arthritis, nerve irritation, or less likely internal organs.

? pleurisy: It may be an inflammation of the lining of the lung. It can cause pain when you try to take a deep breath. Are you having any chest pain, cough, fever? It is important to determine the underlying cause. Go to the emergency department of the nearest hospital. Pleurisy may not be the diagnosis and a physician needs to evaluate you to make sure.