Yes you can.
It doesn't matter how many times you've had sex, how many times you've had you're period and its even possible if you haven't had you're period yet since you start ovulating within the month of your first period.
You can, but it's not definite. If you're safe, and you use condoms or birth control and you know how sex actually works (lol), you'll have a lesser chance of getting pregnant. The only 100% way to not get pregnant though, is abstinence.