As mentioned above by mammo, rectal bleeding is serious and it is never normal. It should be investigated until a firm cause is established and the relevant treatment organised. If the causes are not easily identified by your present medical advisors then I suggest you visit a hospital with a specialist G.I. department (such as the Mayo Clinics - or similar).
You may like to type in rectal bleeding to google and click on to one of the many sites that describe this condition. The Medicinenet site is particularly informative and you will then be better informed for your next visit (hopefully to a specialist G.I. doctor/clinic).
Mayve you should have a repeat colonoscopy??
regards
Morecambe
It sounds like the blood loss is causing all your symptoms, and this is very dangerous. Pain in the abdomen accompanied by blood in the stool and toilet is of real concern. The darker the blood, the higher up in the intestine is where it's coming from, the closer to the anus the brighter red it will be. You can bleed from hemorrhoids (bright red) but with you constant pain and dark blood, somethings not right. But I would think they would have found something with all the testing. Have they ruled out appendicitis? Does the pain on your right side move downward? I wouldn't wait on this, if they say you're bleeding internally, you should be in the hospital. They told you to go, take this seriously.