BC post pregnancy?

Emily • Taken by DTM💕Mommy to ETM❤️
I'm pretty sure I have the right birth control for breast feeding (progestin only) and my little boy will be 8 weeks on Wednesday... Should I take a pregnancy test before I start the pill this Sunday? My SO and I had sex before the 6 week postpartum period was up. Also, has anyone had negative effects with milk production due to progestin only BC?