Tiredness is a very common symptom of early pregnancy. Several hormonal changes occur during pregnancy especially in the first 12 weeks. The high levels of the hormone progesterone may lead to increased sleepiness and fatigue. Feeling tired will not harm you or your baby, but it may cause you to feel very emotional and nauseous.
The best thing to do is listen to your body and try to rest as much as possible. Adequate sleep is also important to overcome the lethargy. Try to also look after yourself and eat a healthy diet. Avoid, or cut down altogether, excess caffeine (coffee, tea, carbonated drinks) as these may prevent you from having a restful sleep.
Tiredness usually subsides around twelve to fourteen weeks as your body adjusts to the pregnancy changes leaving you feel more energised for the remainder of the pregnancy.