Is it common to have low hemoglobin during pregnancy and after csection?

Yes: It's common in pregnancy for women to have lower hemoglobins. Typically your body isn't make fewer red blood cells, but rather there is greater fluid volume in your bloodstream, which dilutes your red blood cells. Definitely following cesarean you will have a lower hemoglobin due to blood loss. So long as you aren't dizzy or feel weak, then you're likely okay. Check with your doc to make sure.