I am a teenager and I want to come out to my mother as bisexual, but she doesn't react well to discussions about LGBT, and constantly says that "those people are only faking it, they're not really gay/lesbian/bi, it's not natural." Her words make me feel very uncomfortable, and make me question myself as well. I am just a teenager after all, but I don't believe it's just "a phase"? I'm not sure what I should do. Maybe I should just never come out?
Your mother is wrong in saying that it is not "natural" to be gay, lesbian or bisexual. She may have been taught that through her religion, or even her own parents, but that is old-school thinking that is just not accurate. It has been scientifically proven that a person's sexuality is determined by their dna. It is a biological determination that begins even before we are born. We all land somewhere on the sexuality scale of either completely straight, completely gay or anywhere in between!
It is natural and normal to fall anywhere on the scale. And who we are, no matter what it is - bi, straight or gay - is absolutely normal and beautiful.
That being said, I'm not sure it is necessary for you to rush into coming out to your mother. You can already see that her response is not going to be great (at least in the beginning) so it would make sense to get yourself in order, feeling strong and proud, before bringing her into the picture. Because when you do, you are going to have to be strong and patient because she will need to travel her path of acceptance. Remember that her love is deep even though she may be struggling with accepting.
There is no rush for you to put a label on yourself. Explore and have fun and you will know when you are ready to come out to her. If it is possible, find an lgbt support group (most schools have them). It will be a great help to have an lgbt family to share your experiences with.
Maybe when you are feeling centered and confident in yourself you can start to question her when she makes her negative comments regarding a person's sexuality. Start getting her thinking about the statements she is making.
When you do come out to her, there is an organization called PFLAG which helps parents and friends of lesbians and gays: http://community.pflag.org/getsupport and they can also help you with information on how to approach her.
Take a deep breath, don't worry so much about labeling yourself right now, or coming out to your mom - and just live, be yourself and no matter what, love who you are.