You have a muscle spasm or tight muscle in your shoulder. when you went swimming it affected the muscles around it as well, making them tighten up in pain and that caused pressure on the nerves going to your hands. Once you release the muscles in your back all these problems should be gone. Here's how to release those muscles:
(do from a sitting position)
Place your left hand on your left leg next to your body. Place your right hand over your left shoulder and find the muscles next to your spine and press on them and hold. After 30 seconds slowly lower your body forward and to the outside of your left leg, keeping your left arm fairly straight as you do. When you reach your lap remain there for another 10 seconds, release the pressure but rest there for another 30 seconds. Then reverse your hand positions and do your right side.
Before doing this take a deep breath and exhale, then try to keep your body this relaxed for best results.