The doctor’s appointment is a good idea. There are really two things to manage: the source of the bleeding and the consequences of the bleeding. As far as the consequences go, if the bleeding has been going on for a while (or the quantity is significant) you could certainly be anemic. That could cause your weakness and paleness. You might want to start an iron supplement, but 1) make sure to let the doctor know, since it can start to change the lab results, and 2) don’t worry when your stool turns black. As far as sources, there are a few possibilities. Cuffitis can cause bleeding, though I think most people have additional symptoms - do you have any pain or bathroom changes? Hemorrhoids can cause plenty of bleeding - have you ever had hemorrhoids before? Are you straining on the toilet?
This is likely to be very manageable. Since we don’t have colons, one of the big worries about bloody stool - colon cancer - is quite rare. Do you have a specific worry, or is it more like “there’s not supposed to be blood there!”?