I am feeling uncomfortable and my wrist hurts me to put my hand in the position requires, why? with a normal mouse i don't have this problem, what am I doing wrong?
could be that your hand is positioned too low in order to put your fingers on the ball area causing you to have to flex the wrist in an non-default position to manipulate it? If so you may prefer the central ball design of the Kensingtons as I do. If you were to rest your hand normally on your mouse in a relaxed position and you put the trackball next to your hand side by side, Do your fingers end up in a position that would, if you simply slid it straight to the side, match up with the proper buttons and positions to be able to navigate or would you need to change the angles or reach with your fingers to accomplish that? If you have to significantly alter the position of your arm or hand from where it is comfortable to use the trackball try one with different ball/button positioning that better suits your personal ergonomics.
Can't stress enough how important it will be to find the one that "fits" your hand or its money wasted. A $200 trackball that is a good match is a much better expense than 5 $19 ones that aren't.
Some say using a trackball is something that takes getting used to, but it shouldn't be painful. I knew immediately which I preferred when I touched ye olde sckool Turbo mouse on the Mac about 15 years ago or whatever. I don't know what people mean by adjusting to how to use one at all.
IMHO If repositioning the trackball itself on the desk or adjusting your seat height doesn't fix the pain, then a different model is definitely in order, though you could try a little "mouse shelf" kind of thing that allows a different mouse height placement from the keyboard surface, but it really does sound like you might be a better candidate for the slimblade or the expert mouse instead.