Thank you for the information,
There are some common causes of such rectal bleeding.The common ones are anal fissures, haemorroids, rectal cancer, anal cancer, colon cancer, colon polyps, etc.
As per the symptoms you have described, the chances of anal fissures should be ruled out first which commonly causes such symptoms and pain just like sitting on a razor.
You should have the relevant investigations done like per rectal examination, sigmoidoscopy, colonoscopy, abdomen sonography, blood counts, ct scan abdomen, etc. to know the associated abnormality after consulting your gastroenterologist or gi surgeon..
The treatment depends on the underlying cause.
Please visit here for more information:
causes of rectal bleeding
Let me know if you have any doubt.