I've had my wacom tablet for 3 years now and I still can't draw on it comfortably. I can't draw straight lines or perfect circles, most of the strokes don't go the way I want them to.

What is the problem here? I know it needs some time get used to but 3 years? (I haven't been practicing so much on digital in these 3 years but still...).
Do you have any tips, exercises, or anything that would help someone increase their control and comfort over his strokes on a tablet? I'm really desperate for anything.

pic related. it's my setup, I have the tablet positioned on the right side, not on middle.