How can I stop my bow string from hiting my arm when I shoot

It could be caused by the draw length on your bow is to long. If its not to long try slightly bending your elbow on the arm you hold the bow with

First of all stop pushing your elbow joint out and that will relief pain and second use a tube-a-grip and then your arm guard further up your arm than usual then lastly when its all settled in buy a full fore-arm arm guard I have went through all of this myself and I'm from the uk and part of the dnaa