Sore Hips

I am 18 and have trouble with my hip joints. If I jar my hip (eg slip on ice but not necessarily fall down), in 2 days or so it becomes incredibly stiff and sore and I even have trouble rolling over in bed or walking at all. It is not sore immediately but gradually becomes unbearable. I have seen a doctor about this but conveniently this hip trouble always seems to run and hide when the doctor is around. They have done blood tests, taken x-rays and mri's but have not been able to make a firm diagnosis. Does anyone else have this trouble, and if you have what have you been given for a diagnosis?