What Does Pain In The Hips On The Left Side Indicate?

pain in the left hip, not just the groin, but when internally and externally rotating. I spend 3 hours a week on the elliptical machine for cardio (vigorously). I am a fitness instructor.... muscles are strong, I teach Pilates, Yoga and Cardio classes. Forward and backward motion is not painful, mostly externally rotating the hip or squeezing the muscles....the entire thigh, outer hip, front and a little of the buttocks, as well as foot becoming numb sometimes. After a deep hip flexor stretch, 3 week ago, it stayed very sore. wondering if I should see a doctor or just ice?, heat? keep working through the pain? Not sure....