In my case it was piles. That or a fissure would probably be the most common explanations.

Has your doctor suggested that there is concern about the cause? I would imagine they would have told you if further tests were necessary. Generally, if bleeding is the only symptom and a colonoscopy rules out cancer, IBD, diverticulitis, etc, there isn't any real cause for worry.

But wouldn't piles show up during the colonoscopy? 

Hi there!

 I am not a doctor. I am pretty sure that piles are almost outside and they can break if the poo is hard. 
As above, try not to worry and make yourself ill. It's not always C. It's very difficult because everywhere is C: on TV, news. 
 

Yes I think I am probably worrying unnecessarily but would love to know for sure what's causing it. I will talk to my doctor. Thank you for your replies! 

Always good to go back and speak to the doctors. There are no silly questions. They know it better.

Good luck!