Can Below The Waist Pain Be Due To A Hip Lesion?

Hi, My mother aged 70 has developed pain below waist. It only occurs when she is standing or walking not while lying or sitting. We saw a doctor who took x-rays of that area. There was nothing suggestive. Her pain is still as it is. Approx 10 yrs ago she has developed a legion on hip area due to side effects of a medicine with steroid. At that time also she felt the pain similar to this. Later it was operated to remove legion and strengthen that are by grating bone from some other area. So we are worried if present pain is similar to that rather than sprain. Please advice.