Bloody mucus in stool and other problems

For nearly two years now i have been experencing incomplete bowel evacuation means do not feel like bowel is fully empty after bowel movement . I also have bloody mucus in stool and blood in stool(at times).These happened for a period of time like a month two months then stopped and again start after somtime. I have had two ultrasound in these years which which did not show any tumor/mass. I am 18 yrs old male and i have not lost any weight all this while but gained weight and my appetite is good. I am afraid of it being colon cancer and this worry is ruinig my daily life and studies. In November i visited a experienced physician who ordered a CT scan which came back clear and did not show any tumor/mass.He told me that it could be due to IBS. He gave me ORNOF and PROVIDAC medecines for some days and after taking them the mucus stopped and have not come till now from then. So should i stop worrying about colon cancer.