Hi!
I think you would naturally feel your wrists weaken at a strengthening, stretching, powerful sports as golf. You said you were slim, perhaps they are just catching up with the new exercise that you have. Believe me, later on, you will overcome it. With the right kinds of golf exercises, warm ups and the correct way of stretching, swinging when golfing, it will surely improve your muscles and it will add more meat to your wrists so that it will be stronger.
