so tired all the time, and look pale.... blood test for anemia came back fine! 30wks. what could it be?

im 30wks and so tired, everytime i sit down i start falling asleep. i told my midwife last week when i seen her and she took some tests for a full blood count... diabetes and anemia, all are fine and normal and said she will test again in 2weeks. what could it be?