Back pain could indicate kidney. Which could explain why blood in the urine. Since there has been both blood in the urine and stool, I would highly suggest being in seen in the ER at this point. If it's all due to infection or some other underlying cause will need to be determined via tests.
Which, Bleeding from the anal area can be due to rectal_bleeding or Gastrointestinal Bleeding
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Another possible reason could be hemorrhoids as well.
bright red blood usually suggest that the blood is coming from the lower part of the GI tract (large bowel or rectum).
But with fever and the bleeding etc., I do suggest being seen for exact cause.
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