It is not of much concern presently whether the bleeding is from within or around the stoma. What should concern us more is the cause of the bleeding. There could be a number of reasons, like late onset liver failure
after transplant (leading to bleeding abnormality), chemotherapy
induced bone marrow
suppression (which decreases the number of platelets in the blood causing bleeding), recurrence of cancer in the remaining bowel, recurrence of Crohn's disease in the remaining bowel. Ruling them out one by one, i suggest you get a liver function test and complete blood count
done. If these are normal, then you should undergo a contrast enhance computerised tomography
(CT Scan) of the abdomen followed by an endoscopy from the stoma. These tests should clinch the diagnosis and the treatment accordingly can be instituted. Meanwhile, it is not a bad idea to show yourself to a surgeon just to rule out a local cause for the bleeding like skin infection/excoriation, etc.