Bloody mucus in stool for 1. 5 yrs.

I am an 18 year old.I have been experiencing bloody mucus in my stool for 1.5 yrs.It happens for some time like month and the it stops then the problem again comes back.I also had feeling of bowel not fully empty after bowel movement for sometime 2 yrs back but it improved.I also got ultrasound two times of abdomen which were OK and did not show any tumor/mass.I am worried about it being colon cancer.I have proper growth and had not lost any weight in all this time. I have a good appetite and do not experience abdominal pain.I observe one thing that this mucus starts to form after a certain change in my diet like when i eat more than usual for some time or eat oily food.So is it linked with my diet.suggestions.