Dog bleeding from rectum?

A few days ago i took my dog for a walk and he could not poop (he did but it seemed like he did it all over himself), that happened a few days later again, and I found what looked like strips of cardboard when cleaning him up...now my sister took him for a walk and said that his was bleeding. He won't let me look at it but it's not gushing or anything, I don't even see any blood...He hasn't defecated in about 2 days...He seems fine otherwise, he eats, drinks, etc. Please tell me what you think might be wrong with him...and I know we need to take him to the vet..but it's not up to me I am only 16 and do not have a job so I can't make financial decisions in my house...