Hi thanks for your question.
You are having this problem since 15 years of age.
Most probably these could be rectal polyps,that bleed while passing hard stool due to constipation
Since these polpys are there for long time ,chances of malignant changes in these polyps are high.
The second possibility is of course haemorrides.
Consult a general surgeon
who will perform proctoscopy/sigmoidoscopy(examinition of your rectum/sigmoid colon
with a cope) on you to differentiate between polyps and haemorrides.
Get them removed whether these are haemorrides or polyps and send these for histopathological examination to rule out malignant changes.
Hope this answers your question.