I often feel numbness on left side of my body including leg, arm and even parts of my face. Any ideas whts this?

See a neurologist. This is an unusual array of symptoms. See a neurologist.
Many reasons. There are many reasons including medications, vitamin deficiency, electrolyte imbalance, anxiety, transient ischemic attack (TIA), stroke, spinal cord injury, etc. See your physician for a full evaluation and physical examination. http://www.nlm.nih.gov/medlineplus/ency/article/003206.htm.