It might be due to the hormonal changes that your body is feeling during pregnancy. Not sure specifically why. I myself felt extremely fatigue from Weeks 20 to Week 23. Once, I dozed off and almost fell off my chair while working on the computer. I did feel slightly better since Week 24 :)
Do let your gynae know and see what she can advice. Our body is undergoing a lot of changes during pregnancy. Make sure you rest well and eat fruits to boost up the vitamins intake!
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