Am I doing the wrong thing?

Yep, you should fast even of your parents and the rest of your family do not. Just because they are not fasting oes not mean you don't have to- you still have to unless you are under/Bar/Bat Mitzvah or have a medical reason that vents you from fasting. Just because they choose to ignore Jewish law does not mean that you also should. In cases like this Jewish law is clear: You obey Jewish law and ignore the fact that your parents are not fasting.

In reality you should fast, the problem is that we do not know your entire situation or even your actual age. The best thing to do would be to contact an Orthodox Rabbi in your community and speak it over with him. He may be able to help you explain to your parents why it is necessary to fast and help you to get permission. It is admirable that you wish to do the right thing, but not always is the right thing as clear as it looks.

Here are some resources to hlep you explain to your parents about the reasons to fast.

FREE lectures, videos and MP3's:

1) aish.com

2) simpletoremember.com

3) ohr.edu

4) horeini.org

5) ncsy.org

6) negia.org

7) ou.org

8) oorah.org

The Halakha is to fast.

However --

it reads to me as if you are just becoming Baal Teshuvah and you are trying to do so while a kid living with non-observant family.

All of the materials I have read about developing observance stress the importance of doing so in a methodical and thorough manner -- not to rush

This is called "the ladder of observance"

Step firmly on one step, then go to the next.

In addition to solidifying your own observance,

if you're a kid living with non-observant parents, you need to keep them comfortible with where you are -- so that religion does not become a conflict.

If you judge the situation carefuly, there will be fewer fights,

they may become supportive,

they may even follow along after you.

But if you push too much - then their opposition may escalate.

Mind you -- I can't see that unobtrusively fasting would cause much conflict.

But this is something you need to judge.

Honor your parents and obey them

If you are fat...fast

If you aren't don't