You can get STDs (sexually transmitted diseases/infections) by having vaginal, anal, or oral sex with someone who has an STD.
The CDC estimates that youth ages 15-24 make up just over 25% of the sexually active population, but account for 50% of the 20 million new STIs occuring in the United States each year.
The CDC recommends that all pregnant women, sexually active women younger than 25, and women who are 25 or older and have a new sexual partner, multiple sex partners, or, a sex partner who has an STD should be tested for chlamydia & gonorrhea every year! Most women who are infected with Chlamydia and Gonorrhea have no symptoms, therefore testing is critical.