Dark blood (brownish to black) doesn't always mean its coming from further up. It could also mean its been held inside for a while until you had your next bowel movement. You can have bright red blood in your stool coming from all the way up from the small intestines. If you see blood of any color then you should contact your GI doctor right away (contact by phone and go from there). You're also having abdominal pain so be sure they know about that as well. If you're having pain in your rectum and anus as well (sounds like you might be) then you should let them know about that as well.
When your GI knows about all of your symptoms (especially your new ones) then they will be able to create the best treatment plan for you. There's no real reason to wait until there's a ton of blood coming out before you inform your GI. If its just as simple as a hemorrhoid then that's great but you're also having abdominal pain which is concerning.