Brief Answer:
Can be a peri-anal abscess.

Detailed Answer:
Hi.
Thanks for your query, read it and understood your problem.

To understand it more I would like to know few more points.

For how many days have you got this lump?
Is it at the anal verge, meaning partially inside and partially at the top ?
Is there any other symptoms like fever ?
How is the consistency of the motion (poop) - is it soft or hard ?
Is there a bleeding anytime?

If this lump you explained is for a few days this can be peri-anal abscess or a Prolapsed thrombosed pile
In rare cases this can be a rectal polyp

Get an early diagnosis by actual examination by a Surgeon.
You may attach a clear picture attached to this query for me to tell you more appropriate diagnosis.

Please feel free to ask for more information.
I am waiting for further information and a picture (if possible) from you.

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Brief Answer:
Most probably an abscess.

Detailed Answer:
Thanks for your feedback.

Pain while using bathroom and when you sit in a certain way indicates that it is most probable a developing abscess.
Piles are not common at young age.

Please get this examined to ascertain the diagnosis and get an appropriate treatment.

You can have a Sitz bath (sitting in a u tub with warm water), it soothes the area .

Wishing you an early and complete recovery.
Feel free to give feedback, you may please rate this answer if you liked it.

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