Constipation is often a problem of pregnancy due to both physical changes and the extra iron you are taking.
In addition to drinking at least six ounces of water a day, try eating
Whole Grain Breads
Whole Grain Cereals
Fresh Fruits and Vegetables
If you are stuck having problems with constipation, you may try a stool softener, such as Colace, a safe option throughout your pregnancy.
For immediate relief, Milk of Magnesia or Magnesium Citrate may be used. However, this may NOT be used on a long term basis.