Blood in stool?

Last monday, when i decapitated there was blood in my feces. When I decapitated again today, there was blood but less blodd than last Monday and there's a strng-like thing in it. My stomach has been aching for the past few days. Could this be something serious?Help me. Puh-lease. Am I dying already? I wanna live a longer life. For Christ's sake I'm still 13.