What Causes High Fever And Lower Back Pain?

My 10 year old son has a fever of 103 and is complaining of lower back pain. To my knowledge, he went to school this morning feeling fine, he is not involved in any physical sporting activities at this time and has had no altercations or accidents today. This is highly unusual, just wondering if you had any idea what this could be or if the symptoms I described are indicative of anything specific or otherwise common?