Pregnancy fatigue often takes a brief reprieve during the second trimester and then returns (often with a vengeance) in the third trimester. You'll need at least eight or nine hours of sleep to have enough energy to get through the day [source: Stokes]. It may help to take a nap, even if it's only for 20 minutes during your lunch hour.
Ironically, although you may yearn to spend the first trimester of pregnancy in bed, by the time you hit the third trimester, it becomes more difficult to sleep comfortably for long stretches of time. If you once slept on your stomach, you must now figure out how to rest in another position. Lying on your left side optimizes blood flow to you and your baby. Try propping a pillow between your knees to support your ever-widening pelvis and place one near your belly for extra comfort [source: Silva].
If you really can't sleep at night -- what with the extra trips to the restroom and the heartburn -- try resting more often during any 24-hour time frame. Napping on your lunch hour, after work and during the nightly news will add up. It also can ease your mind, which may help you rest better at night, too.