Pregnancy Fatigue: Why You're Feeling So Tired and How to Combat It - CNET

• Increased levels of progesterone: “Fatigue is most common in the first trimester as the pregnancy is rapidly growing,” said gynecologist Faina Gelman-Nisanov, MD and Fellow of the American Congress of Obstetricians and Gynecologists. “In a normal pregnancy, the pregnancy hormone, beta-HCG, is doubling every 48 hours. This rapid rise, along with elevations in estrogen and progesterone, creates a common side effect of fatigue that tends to resolve by the 12th week of pregnancy.” 
• Changes in blood sugar and blood pressure: Blood volume also increases to support the developing placenta and fetus, which can make your heart pump faster and with more force, according to John Hopkins Medicine. The Mayo Clinic says different hormones usually keep blood sugar at acceptable levels. Rapid changes in hormone levels during pregnancy can affect the body’s ability to process blood sugar properly.                 
• Emotional and physical adjustments: You also may have very real stress about the lifestyle changes that come with a baby. You may have to adjust to your family growing, which could lead to moving stress or reorganizing your whole home.