I have been on the pill for two years. last prescription i changed brand of pill now back on usual brand. breasts are really sore, could i be pregnant?

Probably not, but...: 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 3 weeks after sex (3 weeks after when conception might have occurred). If taking birth control pills regularly every day, switching brands should not decrease one's protection against pregnancy.