I'm 14
My breast size is D cup now.. And my weight is 50kg..
I was thinking, is it my weight that is making my breast bigger or is it just me..
Can you help me give some tips on making my breast smaller? I really don't want to consider on having surgery as I know that it will be painful and furthermore give me stretch marks.. Please.. :-(

Having breast reduction surgery will not give you stretch marks.

There are excellent bras called "minimizers" that can make you appear to be a full cup size smaller. They are usually quite comfortable.

Take a look here (or just Google "minimizing bras"): Minimizer Bras | BareNecessities.com

Weight can have an affect on breast size, but its not the only factor. But the only way you can reduce the actual size is through surgery. And you will have to wait until you are an adult before any surgeon will do the surgery.