While closing your aiming eye then opening both can help with a short draw flinch, blocking or closing an eye during actual aiming is far too restrictive. When switching hands if you think about it and give yourself time while drawing, you can see or "feel" that you are pointing the arrow correctly. If you shoot with conditioned instinct or partial gap shooting technique like Hill and John Schulz you will soon enough know what your eyes are telling you. I would see a good chiropractor and maybe hit the supplements. Our chiropractor has helped me through shoulder injuries more than once, back when I shot with goofy target form, the injuries actually started because of work related activities and were increased with shooting heavy target bows. Our chiropractor has worked wonders for my wife, I changed the grips on her bows so she can shoot with more of a Hill style now. When shooting, do not jam out the shoulder joints, keep them inline with the target. Hill bent his left arm, this compensates for the offset between the drawing arm/arrow alignment and still keeps the shoulders in line with the target. I have seen lots of shooters over the years shooting with the forward shoulder straight arm technique that ended up hurting both shoulder joints.