The uterus is essential a large muscle, and a very strong one. During the first trimester of your first pregnancy, this muscle is doing the "mother of all work outs"! It is no wonder that you are feeling crampy and achy. If you exercised any other muscle that much over such a short period of time, cramping and pain would not surprise you at all. More pain and cramping can occur while the uterus is growing, and pushing other internal organs out of the way. Ligaments and skin are also stretching slowly or not so slowly, and all of this can contribute to a feeling of discomfort. Cramping generally stops after the first twelve weeks of pregnancy, at the same time other unpleasant symptoms such as fatigue and pregnancy nausea also subside.
Many of the symptoms that are common in the first trimester essentially tell newly pregnant women to take it easy, and relax as much as they can. Making sure you do the best you can to stay healthy is the only thing you can do about abdominal cramping during the first trimester. Dehydration, which is a higher possibility during early pregnancy for many reasons, is something you can work on avoiding by drinking at least two liters of water a day. Taking prenatal vitamins and eating a healthy and balanced diet is something everyone should do, but we all know that that is sometimes easier said than done. Still, paying more attention to what you eat can greatly improve the symptoms you are likely to notice in the first trimester.