If you are having severe abdominal pain in pregnancy, you need to contact a physician. Sometimes the source of severe cramps will be something perfectly normal, like round ligament pain, but other times there may be a condition requiring treatment or even a medical emergency, such as ruptured ectopic pregnancy or appendicitis. In any case of severe abdominal pain, you should see a doctor right away to find out the source. If the pain is so bad that you're not able to conduct your daily routines, and cramps aren't going away with rest, go to the emergency room.
Some amount of abdominal pain is normal during pregnancy. As your uterus grows and stretches, you may feel various types of abdominal cramps ranging from sharp twinges to dull aches that resemble menstrual cramps. The difference is that normal pregnancy cramps usually won't involve extreme pain, and they will usually subside after a few minutes, especially with rest. With any pain that you would label severe, err on the side of caution and see a doctor immediately.
Abdominal Pain or Cramping. March of Dimes. Accessed: Nov 14, 2009. http://www.marchofdimes.com/pnhec/159_15241.asp