Whats wrong with my cat?

My cat Zoey is pooping out globs of blood. (I know its really gross!!) She's been acting her normal playful self except for the blood. And it started out with just little drops of blood in the litter box. What could be wrong with her? (P.S she's always around a hamster, 2 outside dogs and another cat. I don't know if that has to do with anything.) Thanks in advance!! =)