People tend to feel best during the second trimester. The nausea and vomiting is going away, energy is back, and you are not so uncomfortable as you may be in the third trimester.
One of the things that helps get women through the difficulties of the first trimester is to know that most of these difficulties are temporary. Most people feel much better by 13-14 weeks. Women who have lost weight due to nausea and vomiting in the first trimester tend to gain it back in the second trimester. This is a good thing. The loss of energy in the first trimester tends to go away as well. Most women have much more energy in the second trimester of pregnancy.
In the third trimester the uterus will be getting much bigger and take up a lot of room in the abdomen. This can make it difficult to sleep, eat, and even move around. But in the second trimester the uterus is not so big yet, and women are able to do most of the normal activities.
If you are in the first trimester and getting discouraged by the way you feel, just remember that relief is just around the corner. Take advantage of the second trimester; it is a good time to catch up on things you want to do.