Nausea and morning sickness often start around week 6, and may last until around week 14. It is often said that this symptom disappears after the first month, but some women keep on feeling it at later stages. It often comes with vomiting, although there is no reason why they should be associated.
Although the truth is that no one knows for sure what causes nausea and/or morning sickness when a woman is pregnant, some experts relate it to the body changes that the woman experiences after embryo implantation. The body reacting to the effects of hCG, which is the key pregnancy hormone and rises quickly especially during the earliest stages, are a possible cause behind it.
As for food or taste aversions, normally pregnant women tend to go off strong foods and caffeinated drinks, but it varies greatly from woman to woman on a general basis. Again, this pregnancy symptom is related to the hormonal changes of pregnancy.