I am 15 years old and a Christian. I have found to enjoy the feeling of being naked and like to do it when I am alone. But I usually get an erection, and this leads to sexual thoughts, which lead to loss of self-control and judgment, and the next thing I know, I'm masturbating. After it's over, I feel horrible and ashamed that I would have done that. Are there any ways I can resist this temptation, or even not get erections when I'm nude anymore?
It is true that when you are sexually aroused, you ability to make good decisions is inhibited. Thus, you have to make sure that you are not in a sexually stimulating situation unless the result would be proper, such as being with your wife. This is where most guys get into trouble; they tread the edges of improper conduct and then are surprise when they fall in.
I assume that the problem is that you are getting into pornography. If so, then it would be better to avoid private nudity, even though you find it feels good, to avoid the temptation to sin. "But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart. If your right eye causes you to sin, pluck it out and cast it from you; for it is more profitable for you that one of your members perish, than for your whole body to be cast into hell. And if your right hand causes you to sin, cut it off and cast it from you; for it is more profitable for you that one of your members perish, than for your whole body to be cast into hell" (Matthew 5:28-30). Jesus' last two statements are examples of hyperbole -- saying something in the extreme to make a point. He is not saying that people should maim themselves, but that to make the point that hanging on to something that leads you to hell is foolish. Nothing in this world is worth not making it to heaven.