Thank you, everyone! There is nowhere I can find so many supportive people like here!

It has been a while since I last logged in; and when I came back, I felt quite touching to see so many advice from you guys. Reading them made me feel much better!
Actually, I think the problem I have been worried about depends on the culture as well.

In my country, orthognathic surgery is kinda odd, strange; it is nearly the new concept to many people. So if you tell them you're gonna go through that surgery, they will have many exclaimations like, "why do you need that?", "Omg, it sounds so dangerous, you should not do that"... And then I have to explain what my condition is (though I really do not like it). This happened when my mother told some of my relatives about it. Sure there was a big Shock Factor on their faces at that time.
Even braces seem to be "weird" right here. When I got them on, many of my friends kept observing me when (they thought) I did not notice. Once in a while, some inconsiderate people (sadly, including one girl I thought was the closest I had in class) even made fun of my underbite. They talked not behind my back, but in front of me or with me standing near them! Some guys even came to me and told me what was wrong with my teeth. Like I did not know that!

And one girl even asked me why my braces took so long and I did not have any teeth extracted. Why didn't they see me as I am, but instead just focused on my braces and my bite? Though I knew that they really didn't mean to make me sad, those years could have been the worst time of my life. But thanks to my parents and my sweet sister, life was much easier. Thanks to them, I could still stay cheerful in those years.
That's why I really hesitate to tell others about my surgery. Then they will focus on my underbite again, and I don't feel comfortable with that.

But I planned sth like this: after the surgery, if they ask me why I've changed so much, I just tell them that the braces have done a really good job, and my ortho succeeded in pushing my jaw back. That's that! But I don't know if it would work or not. Hope it will!
Again, thank you so much, you guys. Thanks for all the tips and advice. Best of luck to all of you.