Have a cyst on the infraspinatus insertion of my shoulder, would this cause the pain I get in my shoulder and down my arm, also my arm often goes numb?

Probably not. The infraspinatus muscle is one of the four rotator cuff muscles that help to move your shoulder. An abnormality there would typically cause pain in the shoulder with use. Numbness in the arm is a neurological complaint and is most commonly caused by the irritation of a nerve in the neck or a peripheral nerve entrapment syndrome.