Great question. Bleeding from the back passage is actually one of the most common questions that get asked by friends.
In short, the answer is you should see a GP. He 'll be able to determine the source of the bleeding by examining your back passage, and if it' s unclear where the blood is coming from, or if your history is to be able to decide on the necessary further investigations.
In your shoes, I would not be overly concerned. As you mentioned, pain and bleeding in your 20s is most commonly due to anal fissures, caused by passing hard stools. Resolving any constipation issues will help to stop this bleeding.
Painless bleeding is most commonly due to piles, or haemorrhoids. This can be due to constipation, and excessive straining.
Bleeding from the back passage that is associated with colon cancer tends to be mixed in with the stools (rather than fresh blood on wiping, like in your case), or otherwise causes a particular type of stool known as melena (google this) .
My advice for seeing a GP is because it has been going on for some time, and is clearly troubling.
Your GP can easily risk stratify you from your history, do a rectal exam to check where the bleeding is coming from. If necessary, he can then refer you on for a colonscopy to take a close look at your insides, and to rule out colon cancer in particular. You can find out more about colonoscopies in Singapore here.
In the mean time, you can reduce constipation episodes. This will help with the bleeding.
Cheers
