I responded to your question on my blog, but I also wanted to add this, out of pure concern ~ If you're undergoing a fast, you really need to have resources, knowledge and understanding on the subject, especially at your age. There's a lot involved with fasting and you could mess things up with your body pretty bad, if you do it wrong. You could make things worse than before your fast.

A day fast is pretty much o.k. for anyone, but any longer then that, you should have someone who knows all about fasting and your body condition around to help you out.

Kudos for you for thinking about your health, though. It's important to be focused on health from early age. :)