If you are a Christian then you have decided to give your life over to God which means it is not yours for the taking. This website has a great answer to your question and I hope you read it! http://www.bible.com/bibleanswers_result.php?id=228
I will be praying for you and for whatever brought you to ask this question. And I beg you please don't take your life! Try calling hot lines, talk to anyone who can help like counselors, parents, a friend's parents, you can even talk to me. I know it's weird to offer myself, but if you don't know who to talk to I just want you to know you're not alone. I would be honored to help and my mom is also great with advice, the Bible, and faith if you need someone.