Hi.... I Am 7th Month Of Pregnant And I Checked

Hi.... I am 7th month of pregnant and I checked my iron levels on February 11th. That time it was normal and after that my gynaecologist told me to take mashyne-1000. And now I checked my iron levels again last week, it is low. My canada's gynaecologist told me to take another medicine ( preferrin-11 mg). I am confused now what should I do and how come my iron level is low?