Diarrhea and cramping for 7 days, then bloody mucus

I'm a 26 yo female. I've been having diarrhea for the past 7-8 days with bad cramping and sometimes bloating (but without passing gas). The symptoms started 8 hours after eating some sushi with salmon, shrimp and other fish (the diarrhea woke me up at 4 am that next morning) but I'm not sure if it's because of the sushi or not. Since then I've had better and worse days (this Sunday I could barely stand up because of the pain and tension in all my abdomen but was ok when lying down). The next day was better.

Today when wiping after a stool, I saw some blood caught in mucus on the toilet paper. The blood was not bright red nor dark, it was just... normal blood I guess, caught up in the mucus and separated from the actual stool which was soft brown diarrhea.

I'm rather worried about this.

I should mention I had a colonoscopy done less than 2 years ago that showed everything ok. I didn't have diarrhea back then but I was diagnosed with Irritable Bowel Syndrome because I had some pain in my left abdomen (which BTW was probably from my ovary but nevermind ).

What could this be? Could this be cancer or rather an infection?

Thank you for any help!