It comes from the pressure of your growing uterus on your rectum, along with pregnancy hormones, which slow the passage of food through your digestive tract.
Some iron pills can make constipation worse.
Prune juice might also be helpful. Regular exercise like walking, swimming, cycling on a stationary bike, and yoga can all help ease constipation and leave you feeling more fit and healthy besides. As with any source of medical or health care information, you should as a preliminary matter satisfy yourself that the credentials and experience of the source are suitable. The information provided through the Ask the Experts service is a general educational aid designed to help you discuss your unique medical or health concerns with your physician or qualified health care provider. You should not rely on the information as a substitute for personal medical or health care advice, or for diagnosis or treatment purposes.