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Most likely the reason for the blood is that you have hemorrhoids.
There are 2 types of hemorrhoids: internal and external. External ones can be felt as a bulge with your finger and tend to be painful.
Internal hemorrhoids are inside where they can't be felt, don't hurt, and tend to bleed. Hemorrhoids are more common when there is constipation or diarrhea. They are very common.
Colon or rectal cancer can cause bleeding, but they are more common in people over the age of 50. They can occur at age 37, but it would be quite unusual.
The way to know is to see your doctor. A rectal exam and possibly looking in with small scope will reveal whether you have hemorrhoids or any other problem causing the bleeding.
If you do have hemorrhoids, they will often resolve on their own, as long as any constipation is resolved and you have normal bowel movements without straining. Best wishes.