My son breastfed through my pregnancy with my daughter, and now they are both tandem feeding during this pregnancy. I didn't find it affected my morning sickness at all. My supply definitely goes down when pregnant so my daughter has priority as she's younger, and I'm not even sure if my son actually gets much (if anything) but he still likes to feed once or twice a day. I also have a number of months during the pregnancy when breastfeeding it absolutely excruciating. I've been known to cry out in pain or actually cry while feeding, but I know it will ease (and has started to do so thankfully).