time will take care of the pain. would like to see a video of your swing you say your coming over the top with a 3/4 8 iron, your doing some thing wrong cant happen on a 3/4 swing. sounds like your arm is bending to much. i can tell from your post your trying to hit the ball way to hard, it doesn't take a lot of power to hit the ball, slow down a bit and work on keep arm and back straight, ( that's why your arm and shoulder hurt not from hitting the ground) your using muscles that you normally don't use so its making them sore, i know this from experience. slow down your swing work on concentrate on keeping head still and getting a good wrist cock and and good shoulder turn, keep it easy and smooth with good rhythm it the fastest way to learn and the ball will still go just as far if not farther. try hitting some balls with your feet real close together that forces you to slow down to keep balance.