Hurts to breath on left side at the top of my back?

May be muscle spasm: Sometimes a nerve gets "pinched" as it leaves a vertebra and will cause pain and/or muscle spasm. When you breath in your chest and upper back muscle move and may also irritate that nerve. I would advise consulting with an osteopathic physician. If you were a long time smoker i might be more concerned but at 26 that diagnosis is way down at the bottom of the list. Anyway you should not be smoking.