HELP!!!! Please

So my boyfriend and I are ready to have sex for the first time. He's 18 and I'm 16. I'm just scared about it hurting. I don't want it to hurt. He keeps asking me if there's anything he can do to help with the pain. But idk what to tell him. I need advice on if there is a way. And also what can I do for precautions to insure I don't get pregnant. Well what can we both do? Like day after pills without my mom finding out I bought it. Since I can't exactly buy birth control at my age. Please help. 🙏