Cramping can be very common during pregnancy, and can be caused by many things. Frequently, cramping is caused by the uterus getting used to a baby growing and moving, especially in the third trimester. Usually it will feel similar to period cramps. If beyond the first trimester there is any bleeding beyond just spotting with the cramps, regularly occurring pain, or very severe pain (i.e. sharp pain or pain that keeps you from performing daily activities), then you should speak with your doctor.