Every time I have a poo on the tissue blood have been there, I felt and there is a small bump, it's quite sore. This has gone on for about 2 weeks now. Is it piles or something serious.?

Likely not cancer. When someone asks if something is serious, they frequently mean "Is it cancer?' In a 16 yr old, it's likely not cancer, but rather either an anal fissure or a hemorrhoid. Fissures typically occur after constipation or trauma, and if treatment with stool softeners doesn't help after a month, surgery is often required. Hemorrhoids (piles) may or may not need surgery. You need an exam by a doctor.