Constipation is a common problem in pregnancy. Most to-be mothers will experience at least transient constipation during their 9 months. Regardless, I would discuss this with your
ob/gyn who can help ensure there is no other cause and can help treat it safely.
There are a few reasons why pregnant women become pregnant. One of the reasons is the direct effect of the gravid uterus. As your uterus expands to accommodate your growing child, the uterus can press on adjacent organs. If it presses on the rectum it can cause constipation. It can also press on the bladder that makes some women feel the need to pee more often. The other reason that women become constipated in pregnancy is that the hormone progesterone is at a high level during pregnancy. This hormone causes smooth muscle relaxation--which makes it harder for your colon to move the stool outward.
In order to treat the constipation, your ob/gyn may recommend a few therapies. Drinking plenty of water, exercising, and eating high fiber foods are all important. Vegetables, meats, beans and grains all contain fiber. I would avoid laxatives unless specifically cleared by your ob/gyn.
Talk to your ob/gyn. He or she can talk to you more about constipation in pregnancy.