There just seems to be a lot of extra tension in your shot. You're leaning into it, your bow arm is locked, and you seem to be muscling the string into anchor. You're a big guy with big arms, you shouldn't have to work so hard!
Try standing straight and drawing where your arms feel relaxed and the only tension is in your back as you draw with your elbow (like your hand is just a string-hook). Shoot a few times with the focus being entirely on that feeling. Then try it sitting down on a chair. Your back and shoulders should be able to remain relaxed and aligned sitting, standing, kneeling, what have you.
I had issues with flailing bow arm and I was doing most of the same things (leaning, forcing the string into anchor, a lot of tension in the bow arm). It took me a few days to get the feel of drawing with my arms being relaxed, and I have to check up on it once in a while, but it makes a world of difference!