I encourage you not to masturbate if at all possible. Sexual stimulation has its place, but within the marriage bed is still best. Protect yourself in the area of sexual health by not inserting anything into your private areas. Self-control is very healthy for young people and waiting to satisfy your sexual urges until you have married is really a blessing. Try to find other things to keep your attention, like hobbies and sports, spending time with friends and family, and doing things that challenge you physically and mentally. Do not look at pornography or sexually stimulating photos as this causes a host of problems that people are often not prepared to deal with. Keep yourself pure. There is more to life than sex. Did you know that people talk 95% of the time about something they do only 2-5% of the time. That is a lot of wasted talk. There are much more positive things to read and talk about than masturbation. Humans are sexual beings but our focus should not be so much on the unhealthy fulfillment of these urges, but rather on how we can do things in proper order so that our lives have the blessing that God intended for us. Staying pure in this area can help you immensely when you do get married.
Ignore the above poster please...
No, you cannot get pregnant from masturbating (unless you're doing it with a guy and you get sperm in your vagina, I guess).
Read the "MASTURBATION FAQ" thread for more ideas...