In pregnancy, the hormones released make ligament lax and leads to stretching creating pressure on lower back spine. Includes extra demand of foetus on mother. If there is no other factor like trauma or injury or any bone disease, conservative approach can be tried like good posture, hot fomentation. If it's very severe, consultation is advised. If not possible, Plain paracetamol can be used. Danger signs like bleeding, spotting or burning urination need to be watched for