[Astro04]

Why is it so big?
How big will it get? (Since its of course still growing rapidly)
Is there anything wrong with it? Disfunctions?
What underwears should i use to be comfortable?

To answer them:

Why is it so big?
It could be different things, but you're too young to say the final sentence. Do you had some parents with similar things?

How big will it get?
That's unknown... i can't say it with precision now.

Is there anything wrong with it? Disfunctions?
In fact, the main disfunction you will have is to find something to put on for your size. Except of the shyness (that will be pretty understandable.)

What underwears should i use to be comfortable?
For now you can use large boxers. or large swimsuits.

Hope it will help.