It is possible that, rather than being pregnant, your periods are so irregular that you think you are pregnant because you haven't had a period in a long time. Some young girls only have one period per season for a long time because their bodies are taking a while getting used to puberty. If there has been no sexual activity, there is no baby. That is that! If there has been a bit of sexuality, even without going all the way, or if he withdraws before orgasm, pregnancy can happen because sperm is present. There are a lot of them and they all like to swim.