In pregnancy its high oestrogen stimulating the foetus that causes the morning sickness in the first trimester, more detail is below from Wikipedia, but you could be getting the progesterone acid reflux which can make you feel sick and hungry due to the excess acid as mentioned here too as there are so many different types of nausea:
Pathophysiology of vomiting in pregnancy
An increase in the circulating level of the hormone estrogen.[9] However, there is no consistent evidence of differences in estrogen levels and levels of bilirubin between women that experience sickness and those that do not.[10] Related to increased estrogen levels, a similar form of nausea is also seen in some women who use hormonal contraception or hormone replacement therapy.
An increase in progesterone relaxes the muscles in the uterus, which prevents early childbirth, but may also relax the stomach and intestines, leading to excess stomach acids and gastroesophageal reflux disease (GERD).
An increase in human chorionic gonadotropin. It is probably not the human chorionic gonadotropin itself that causes the nausea. More likely, it is the human chorionic gonadotropin stimulating the maternal ovaries to secrete estrogen, which in turn causes the nausea.