Yes, being very tired during the first trimester is normal. Your body is trying to make a new human being. Perhaps you didn't notice it as much with your previous pregnancies because you were not chasing two kids. The vast majority of growth for a fetus is during the first trimester. If the baby kept growing at that rate, you would give birth to a very, very large baby. Because your body is working so hard to grow the baby, you will feel pretty exhausted. try to rest, find someone to take the boys for a couple of hours, and seek help with the household duties for a time. that should help a bit.