[Eternal]

Did you take the pregnancy test at least two weeks since you last had sex and did you take it with your first pee of the day? If not, then it's not going to be accurate. Also false negatives are not really common, if they were nobody would take pregnancy tests. False negatives really only happen if they are used incorrectly or too early.
Also I wouldn't worry about being pregnant if your period is only 3 days late. Lots of things can make periods late such as stress, exercise, etc. And because you're only 17 it's not going to be too regular yet, either. In fact periods are never super on the dot anyway. Cycles typically aren't ___ number of days, they will fluctuate each month. Being underweight can definitely make your period late or even stop coming.
Symptoms typically don't occur until a few weeks after your pregnant, but you may notice your breasts are tender after a week since the egg got fertilized.
My best advice is to wait another week and if your period still isn't here, take another test. And use condoms if you're going to have sex. The pull-out method is not a safe way to prevent pregnancy and it's more risky than it's worth.