What Causes Yellowish Mucus In Stool?

I'm at 24 year old female and over the last month I've had a change in bowel movement and have been noticing yellowish mucus in my stool at least once a day. Haven't noticed any blood , feel like I've been straining more and I have no hard stool. Just loose and I am very worried I went to a doctor and he said either IBS or colitis but I was hoping for another opinion