Two of the most common symptoms in early pregnancy are fatigue and nausea. Fatigue you can only fight for so long before your body forces you to rest. Fortunately, this period will pass soon. Later in pregnancy, you even will find renewed reserves of energy, especially during the "nesting” stage. For now, get the rest you need as your schedule allows. Keep in mind that the schedule you set during pregnancy is the one your baby will be inclined to follow after birth, so if you don't want to be up with a baby watching talk shows at 02:00, don't stay up and watch them now.
Nausea in pregnancy often is referred to as "morning sickness,” but it can strike any time of day, and sometimes all day. Eat mild food as often as you feel like it. Your doctor might suggest a nutritional supplement as well.
Some women don't suffer from either of these symptoms and yet have perfectly healthy pregnancies. Other "non-symptoms” include weight gain and cessation of menstrual periods. While some women seem to "show” almost as soon as they find out they're pregnant, others skate by with nary a sign into their third trimester. As long as your doctor says you and the baby are healthy and getting enough nutrition, don't worry about it.
Similarly, while for many women the first sign they are pregnant is a missed period, for others that's not the case. How do you think women get to be four and five months pregnant without knowing? In some cases, menstrual periods have continued until about 18 weeks of pregnancy … and the babies turned out just fine.
If you are concerned over your health at any point, talk to your midwife or doctor. It is better to feel silly than to make yourself sick with worry.