A nap or a few extra hours of sleep is a requirement, not an option. Your body is working overtime to produce more blood and pregnancy hormones -- all with the goal of developing a healthy baby. In addition, your body's level of progesterone is at an all-time high. This may make you feel especially sleepy during certain times of the day or evening.
The rest of the time, you may be tempted to take on new projects because you're feeling hints of energy during this phase of pregnancy. So, it's even more important for your partner to encourage you to build rest periods into your daily routine. He should also take an active role in meal preparation, ensuring you have a balance of iron, proteins and essential vitamins and minerals at your disposal.
Even if your energy level feels good, don't be shy about asking for help. Detail specific needs to your partner, rather than vague requests. Trade "I need your help around the house" for "Please load the dishwasher every evening."