What are some reasons teens bleed when they poop?

Hi im 15 years old and today when i went poop blood came out, it was bright red. When i went it felt like a tear maybe cause the stool was hard? Well i took a urine test before this happend and it came out good but before the urine test the same thing happend , blood came out when i pooped but then stopped. What can it be? Any advice?