It's impossible to know exactly when you could get pregnant, Amanda. Here's why: You're most fertile around the day you ovulate—which, if you have a regular 28-day cycle, is any day between days 10 and 17 (counting from the first day of your last period). Since sperm can stay alive inside your body for up to 72 hours, though, that means if you have sex on day 7, you could get pregnant three days later, when you ovulate. Plus, many women ovulate at other times of the month, so there's no way for them to know when they could get pregnant. That means even if your cycle is regular, it's always risky to try to calculate when you could get pregnant. You never know for sure.

No. Semen can only fertilize an egg and result in pregnancy if it enters through your vagina. But although swallowing semen can't get you pregnant, it still puts you at risk for disease. Many STDs (like HPV, herpes, and gonorrhea) can be spread through mouth-genital contact. So always use a condom to decrease risk.

It's a slang term that means a girl's hymen has been torn by losing her virginity. The hymen is a thin layer of skin around the opening of your vagina. Most doctors agree that the hymen has no physiological function. At some point in life, Alex, your hymen will tear— but it can happen through any physical activity, not just intercourse. Lots of girls don't even notice because it happens while they're playing sports or inserting a tampon. If your hymen is intact when you have intercourse for the first time, it can be uncomfortable and cause you to bleed a little—and because of the blood, some (crude!) people refer to it as "popping the cherry."

Studies show that more than 70 percent of girls masturbate by the time they're 18; they just don't talk about it the way guys do because girls tend to be ashamed of it. But there's no reason to feel ashamed. Masturbation is a healthy way to learn about your body and what feels good for you. A girl masturbates by touching herself and rubbing her clitoris (a sensitive pea-sized organ at the top of the labia) with her fingers, sometimes bringing herself to orgasm. But there's no "right" way to masturbate. If it feels good, then you're doing just fine.