In the past I have experienced an occasional cramp in my hips when keeping my leg on to go forward to trot or to keep up the horse's speed . But in my last lesson, with a larger horse I had never ridden before, it was much more frequent, always on my outside leg and under the same circumstances I have described before (basically when I had to lift my legs away from the saddle. The horse I was riding didn't react when pressure was applied by the legs, so I had to kick quite strongly...). It feels like my hip joint is out of place, and hurts like a cramp. So my instructor got me to ride with no stirrups, and it was fine.
I wear denim jodphurs which my be too tight around the hips, I was quite thirsty, and it was very cold. Any ideas as to what's causing it, and how I can stop it? Anyone else experienced this?