Had unprotected sex 3 weeks before expected period, 2-3 days after period ended, about 6 days before ovulation. Should I be worried about pregnancy?

Not if you're... Not if you're trying to get pregnant. Otherwise, yes. A urine pregnancy test, done correctly, gives a reliable result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon. If a woman gets her normal regular period, then she is not pregnant.