Cat keeps going potty on my bed?

I used to have my cat sleep in my room. But lately she has been peeing on my bed! So i keep her out of my room at night. And once she pooped on my sisters bed. But just today i brought her in my room because i wont ohn my bed on my laptop and so i figured she wouldnt do anything since im watching her. But sure enough i leaned back to lay down, and my bd was wet. She managed to pee while i was on the bed with her, without me noticing! I dont know whats wrong with her! help?