Well one thing is for sure. Your not old enough to be having sex or you sure would know the answer to this question. But I will tell you, no you wont get pregnant if he goes in his underwear. Why don't you wait a few years and not be another one of those who seeks support from welfare because you were to stupid to practice safe sex because you didnt even know about it. You have a whole life ahead of you and don't you have any dreams other than being a parent at your age and then your life is all over.