Sore breasts for 3 weeks now light spotting 5 days before my period is due...could it be pregnancy?

Maybe. Maybe not.: It can be hard to tell if a woman is pregnant because some of the symptoms seen in early pregnancy can also happen in non-pregnant women. A urine pregnancy test gives a reliable result if done correctly. One can test about 3 weeks after sex (3 weeks after when conception might have occurred), 1 week after missing a period, or 1 week after starting a "weird" period.