Why is my 9 week old kitten bleeding from her behind?!

I’ve been taking care of all my kittens since they were born, but recently I’ve been noticing that there were blood spots on my floor almost everywhere.I figured that it was one of the mothers bleeding from after giving birth.But then I thought, the mothers wouldn’t still be bleeding after nine weeks.And I would then go to my litter box and see no blood, but I would still find blood spots on my bedroom floor.So I figured that one of the cats had gotten a scratch from playing with one another.But later on, that still didn’t make since to me.So one day while cleaning my room I picked up one of the calicoes and she felt real poky on her tail.So I looked and her bottom was all red.Her feet and everything were covered in blood.I then realized that this was probably why she had always been so tired and kinda not wanting to play anymore all that much.And now I don’t know what to do.I want to do whats best for her and the other, but I just don’t know how.Oh please help me.Please, if you know what’s wrong with my kitten, please tell me why shes doing this and what I should do to help her.