Need Medication For Pain In Flank

My mom has dealt with some sudden and severe pain periodically for a while now. She may go a month without having the pain and then all of sudden it begins again. Sometimes when this happens it will hurt severely for about 30 minutes to an hour and then ease away. The pain, as she describes it, in her flank or her lower side, feels as though something is going to burst. What does this sound like?