sudden weight loss in pregnancy

I am afraid. My sister's pregnancy is not going well. She has suddenly lost a lot of weight. She feels nausea and she is vomiting all the time. She says it is normal for pregnancy to vomit, but I not sure that it should be so often. I can't make her go to the doctor. Can you tell me why she is experiencing sudden weight loss in pregnancy?

I must say that your sister is acting irresponsibly. How old is she? She must realize that she is responsible for two lives not just one! By symptoms you have described it is possible that she has hyperemesis gravidarum. It is condition in which pregnant women lose the fluids and weight by ongoing vomiting. It can lead to dehydration. It can have severe consequences on her baby. She must go to a hospital so she can receive intravenous fluids and to stop eating or drinking for some time to calm the stomach and then to start eating slowly.