If your string is slapping your arm, that can be as sign that your draw length is too long. Not written in stone by any means, but that could be part of the problem.

But don't give up. Lots of the guys on here will be willing to help you. I also would suggest you post a picture of yourself at full draw. A shooting coach is also a great idea. Also the guys down at the local bow shop can very vety helpful in pointing out what you're doing wrong.