I am 7 weeks pregnant and nursing a 6 month old. Should I stop nursing during pregnancy?

Not necessarily. If/when the kid makes short work of feeds it may be an opportunity to stop & get ready for the new one. Weaning before the next one comes along helps diminish the displacement/competition issues. There is also a difference in your milk with early/ mature production. That said, some moms just keep on feeding and add the new one to the rotation. It is all in how you feel.
Pregnancy and lactat. You can continue breastfeeding while pregnant as long as the pregnancy is uncomplicated. Make sure you are taking sufficient vitamins and an adequate diet. If you are having threatened preterm labor best to stop as the nipple stimulation releases oxytocin which can increase the contractions.