My first instinct is to say you are riding backseat, and not centering your weight on the board. When riding hardpack, I feel like your front leg should burn a bit, if your back leg feels tired, you are backseating while riding.
Edit: also make sure you have your foot centered on the board with equal toe and heel overhang.
Ive been watching some stuff on youtube and they say to basically apply more weight on the front foot and almost steer with the back like the rudder of a ship.. I am gonna work on this a lot sunday