Dear Chen,
    This may or may not help.  I had a similar problem with my second baby.
My family doctor decided that I was semi-dehydrated.  I was drinking plenty
of other fluids, however I was not consuming very much water.  I felt just
like I was having morning sickness.  I did start drinking more water and the
symptoms went away.  I haven't had a baby in eleven years but occasionally I
go full steam ahead and forget my water.  On those days I usually feel a
dull headache first and if I ignore it I will become nauseated.
Sincerely,
Marguerite Kelly, IBCLC
"When I count my blessings, I count you*Twice*."