Red Blood In Stools And Pain On Left Side, Uncomfortable, Tiredness. Awaited Colonoscopy. Can This Be Cancer?

Hi, I am a 24yr female engineer. I sometimes have red blood in my stools (no constipation/pain) and occasional pain in my left side. When I visit the toilet, I usually feel as if I still have some left in my bowel - v. uncomfy feeling. This has been going on for the past 7 months now - intensifying. The worst thing is constant tiredness. I consulted two Gastroenterologists and they both suspect cancer (after an *cough* examination, one of them said he spotted polyps?) because my mom had breast cancer . They want me to do colonoscopy but my mom and uncle have had them done and it was so painful. Can I be experiencing some other symptom? Is there an alternative to colonoscopy? I can t believe I m asking this on the internet, but feeling pretty ill today (very rare), browsed the web and found this great site so gave it a shot! :)