When I started I was often tired out too. That will change as you improve your technique. Try practicing lots of S turns to get smoother. It helps to think about the edges of your board when riding to get an understanding of how you are turning and how you can work with the board instead of thrashing muscles working against it.
Try setting the back binding to 0 or even plus 1 -5, this will help with turning more efficiently at first. Switch and crazy duck settings can come later.
Also, if you haven't already, get up to the blue/red steeper runs as thinking about edge hold easier to concieve with a bit of gradient.