Two thirds of women will experience morning sickness during their first trimester, and almost half may have morning sickness even as late as the third trimester. Morning sickness is clearly related to your hormones. There is limited safety information on prescription medications during pregnancy to treat this. You can take pyridoxine or Vitamin B-6. This is presumed safe and can be effective. Ginger seems to settle the stomach and is also presumed safe in pregnancy. You can get crystallized ginger at the grocery store in the spice aisle.
If you feel nauseous and do not feel like eating, make sure you stay well hydrated and drink plenty of fluids. It is not uncommon for women to lose weight during their first trimester. It is much more important to eat adequate amounts of healthy foods during the second and third trimester. Do not let yourself get worried if you suffer from morning sickness in the first trimester. But always talk to your OB about any of your concerns.