Bristol Palin’s pretty, lightly freckled face was nowhere to be seen on the overhead screen as images from her high-school senior slideshow – photos from the prom and a Class of 2009 portrait set against the Alaska snow – played during May 14′s Wasilla High commencement ceremony.

Did it make her sad to have missed out on so much senior-year fun – to be spending graduation night not with a gang of friends but at home, giving her 5-month-old son a bottle while her extended family plays “Eskimo bingo”?

Bristol, the eldest daughter of Alaska GOP Gov. Sarah Palin’s five children, answers with a multitasking mom’s whiff of impatience: “I have other things to worry about.”

Bristol Palin, 18, has logged more of those “other things” than some people twice her age. In just the past nine months, she weathered her mother’s bruising vice-presidential run; a failed engagement to boyfriend Levi Johnston that played out in the national media; and, most indelibly, a pregnancy that made her both mother and poster child. She is uncertain where she will go to college – she’s thinking of a two-year business program – but says her near future will include advocating for teen-pregnancy prevention.

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“Girls need to imagine and picture their life with a screaming newborn baby and then think before they have sex,” she tells PEOPLE. “Think about the consequences.”

Her mom may be governor, but there is no nanny in the Palin house. Bristol gets up – usually twice during the night – to feed Tripp, who sleeps in a hand-me-down crib in her bedroom, and she says she has tapped out at least one school paper with her son crying in the background. She breastfed her baby for a month, pumping milk before class and rushing straight home to feed him. And she worked two part-time jobs to help pay for the diapers and formula her parents otherwise supply.

“If girls realized the consequences of sex, nobody would be having sex,” says Bristol, sitting at her parents’ lakeside patio table. “Trust me. Nobody.”

As for her breakup with Levi, 19, with whom she’s still trying to resolve child support and visitation issues, Bristol says it was for the best. “I’m thankful we didn’t get married because if it wasn’t going to work now, it wasn’t going to work in five years.”

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