I am 13 and I have 36D bra size and everyone is making fun of me at school. I just can't deal with them they are to big and I try to hide them but they are just to big.

I am sorry you are having trouble with being who you are.
But you know what, the people who are making fun of you, would do so, if you had small ones, or if you had bad hair, or bad clothes.

It is learning to deal with loving who you are and not worrying about what others think.

Next at 13 you are too young to do anything medically about this. After you become older, you may decide for surgery but that will be personal choice, ( esp since most insurance does not pay for it)