Recently I started riding again, western. Whenever I have my feet in the (hopefully) correct position, the outside of my ankle hurts like h***. When I dismount, my knee is usually sore until I walk on it a bit.
I keep my feet with heels down, toes up, with the balls of my feet in the stirrup. It just hurts, and only on the one side. Drives me nuts. I try to keep the weight off the stirrup, and have a deep, light seat using the upper leg. Back is straight but not rigid (I can't do rigid, or to inwardly curved due to a past injury, heh).
Perhaps I'm doing it wrong...I dunno, that's how I was taught >-<