At your age, it is highly unlikely that the lump you felt is a rectal polyp or growth.
From your description, I think you may be having a thrombosed piles which can remain painful for sometime.
Simple piles treatment from your family doctor may help with the condition.
However, if the pain persist or discharge start to occur at the problematic site, consider getting a review with a specialist for treatment.
At times, a minor surgical procedure may be needed to address the problem. I wish you a speedy recovery.
-Dr Quan
