Around half of all pregnant women experience nausea and vomiting, and around 3 in 10 women experience nausea without vomiting. For most women who have morning sickness, the symptoms start around six weeks after their last period. Read more about coping with nausea and morning sickness in pregnancy. If you're being sick all the time and can't keep anything down, contact your GP. The pregnancy condition hyperemesis gravidarum (HG) is a serious condition that causes severe vomiting and needs treatment.