Popsider, maybe try incorporating a bit of walking/running backwards, walking sideways (scissor movements) and walking/"dancing" at 45 degrees to forwards, into your exercise routines, to strengthen the muscles at the sides and at the back of your hips, in case there is a muscle imbalance there. Running mainly works the muscles at the top front of your legs but not the muscles at the sides.
(You could also do some scissor movements with your legs in the deep end of the swimming pool for the same purpose.)
Also consider seeing your GP and arranging an x-ray of your hip.