Are you having any abdominal pain, or pain when you go to the bathroom? There are a couple things that it could be like Crohn's, or ulcerative colitis. It could also be something like hemorroids, but it doesn't sound like you have been straining to have a bowel movement. I would suggest making an appointment with a GI doctor because it could be something serious as the conditions I listed above. In either case, there are treatments to help with those issues.
I am so sorry you are experiencing such symptoms. I can only imagine how scary that must be. Hang in there.
You need to see a gastroenterologist. It sounds like you might have an inflammatory bowel disease like ulcerative colitis. You need to get a diagnosis and treatment and treat any anemia you may have.
There is always concern when there is blood in your stool. The good thing is at your age you can head off anything before it gets serious. See a GI doctor and go from there. Good luck!