Like said above check your grip !!!
Try this... grip your bow with a full fist (like you would hold a baseball bat or hammer with one hand) and hold the bow out in front of you, look at your elbow it will be in close to where the string will be traveling when you pull the trigger. Now grip your bow the correct way ..knuckles at a 45degree with a loose grip, the grip of the bow should be in the meaty part of your hand, now look at your elbow it will be turned away from the string when you pull the trigger. Hope it all makes scense to you ....bottom line, the correct draw and the correct grip and you will never hit your arm with the string.