Thanks for writing to health care magic.
If this is going on since long time he requires further investigations.
Most probably he might have had repeated courses of antibiotics by now.
I think a local examination of the anal region followed by rectoscopy and if required colonoscopy
will help in identifying the cause.
Was that fresh blood associated with the stool or is it altered blood?
Do you see any drops of blood associated with stool?
Please reply so that we can help you better.