HELP mEEEEEEEEEE!!!!?

when i tried having a bowel movement which i did.. i saw mucusy blood..not dark blood but very light blood.. and sometime streaks on the stool itself! ive been to doctors and they told me not to wry(gastrologist) and told me they dont think its anything bc i was under a lot of stress.. i tested positive for occult blood in my stool however did not put doctors @ alarm.. suffer left side pain.. im only 20 any ideas??????? PLEASE HELP ME!