Lumbo-pelvic pain is a common and non-specific problem during pregnancy and postpartum. Although perinatal pyogenic sacroiliitis is uncommon during this time, it might be difficult to distinguish from reactive sacroiliitis in women who are experiencing significant lower back and pelvic girdle pain, as the symptoms and signs are not clear and the tests are not definitive. A 34-year-old primigravida went to the emergency department with severe lower back pain radiating to the right gluteal region and down to the back of the right thigh. This pain began 12 days prior to her presentation and eventually worsened to the point that she could not stand or walk. Her vital signs were within normal ranges, and she was experiencing a fever. Apart from a slight widening of the symphysis pubis, her pelvic and lumbo-sacral pain X-rays revealed no important findings. With the clinical impression of right lumbo-pelvic pain, the patient was admitted for pain management and further inquiries. Despite the fact that the antibiotherapy was prescribed to treat a urinary tract infection, the significant recovery of the patient's symptoms, even in the absence of a definitive culture of aspirate from the right sacroiliac joint, supported the diagnosis of pyogenic sacroiliitis.