A prolonged bleeding from rectum and your other symptoms like pain; needs investigations and a physical examination by either a gastroenterologist or a surgeon. The common causes can be;
1) Hemorrhoids or piles (inflamed)
2) Anal fissure
3) Polyp rectum
5) Inflammatory bowel disease like crohn's disease
6) Growth in rectum or colon
Investigations needed to establish the cause are;
3) Barium enema
Read this resource;
If you can seek an appointment with a gastroenterologist in couple of days; you may wait. Otherwise go to ER for an evaluation. With a history of psoriatic arthritis, ulcerative colitis or Crohn's disease, apart from inflamed piles are the most likely diagnosis in your case.
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.
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