Don't worry — what you're describing is called round ligament pain, and is totally normal. Here's what's happening: During pregnancy, your uterus expands from the about the size of an apple to the size of a watermelon. The ligaments that surround and support your uterus and connect it to your groin (collectively called round ligaments) have to stretch and thicken to accommodate these changes, and this can hurt a bit, especially in the second trimester. It feels like sharp pains in your abdomen or hips, and often increases when you move quickly, go from sitting to standing, cough, or laugh.
To alleviate round ligament pain, try switching positions or propping up your feet to rest for a while. It might also help to simply slow down your movements to give those ligaments more time to adjust. Your doc may suggest some gentle stretches (or even a couple of Tylenol caplets) if you're feeling the pains often. You shouldn't worry unless the pain last longer than a few minutes, is severe, or is accompanied by any bleeding, strange vaginal discharge, or other unusual signs. If any of this occurs, call your doc asap.