Last night I noticed a lot of blood in my poop and I am had this before when I was about 6 and I am only sixteen my mother was told bye the doctors if happens again to come back but she is hesitating on wheather or not to take me... what could be the cause of this?

There are too many things that it could be, we cannot give you a diagnosis over the internet. You don't need guesses, you need a diagnosis.

Go back to the doctor, this may be nothing, but if it's serious then it's important to have it checked out now.

Good luck.

This could be colon polyps, this could be ulcers, cancer, or irratible bowel syndrome caused by stress. But you must, must go to the doctor. They will do a colonoscopy, or sigmoidoscomy probably... It very well could be something totally different than when you were 6 years old. But it is something that needs to be looked into immediately! Youi need to go to a doctor who specializes in gastroentermology.