My Mother Has Been Experiencing Pain On Her Left Side

my mother has been experiencing pain on her left side lower back almost near the wing that generates under her right rib cage. the pain at night becomes so excruciating. The dr prescribed a low dose of percoset. It works for a short time but the pain never really goes away. The er ruled out kidney stones and she was given meds for a slight uti and nerve pain. This has been going on 3 weeks now and seems to be getting worse. Thank-you what is your suggestion?