There are several great ways to stay regular during pregnancy, though I recommend herbs last. Eat a plant-based diet to ensure optimal nutrition, including five or more servings a day of fruits in season, vegetables (raw salads and cooked vegetables), and one to two servings of whole grains that suit you.
Supplement with plant proteins such as cooked garbanzos tossed on summer salads, split pea soup when weather turns cooler, and every lentil or bean you like (be sure to cook with aromatic herbs and spices to make them more easily digested).
All that fiber and adequate hydration will keep you regular and feeling satisfied as your appetite naturally goes up during pregnancy. Whether you include animal protein is up to you, so I'll just note that excess cheese or red meat can contribute to constipation. Too much bread or the refined sugar-and-flour sweets some women seem to crave can lead to a sense of bloating, indigestion, or constipation as well.
Plain water and soothing herb teas such as raspberry leaf, nettle leaf, lemon balm, ginger root, dandelion leaf and/or root, rooibos, fennel seed, and lemon verbena are just a few of the teas that pregnant women have been enjoying hot or cold for centuries, along with plain water. I like mine with a dash of fresh lemon juice added. We also offer a Pregnancy Tonic Herbal Tea Blend for this specific purpose.
In addition, maintaining regular digestive function depends on movement. I would also recommend some light form of exercise, even if just walking. Tailor your activity to take into account some natural spells of fatigue as your pregnancy progresses. Many studies show exercise and fitness reduces complications at the time of birth, for mother and baby. The general guideline is to try a teaspoon of dried leaves in a cup of water just off the boil, covered, to steep 5-15 minutes. Strain the tea leaves and enjoy a single herb or a mix and match according to your palate. If it tastes too strong, you can always dilute with plain water until it tastes good to you.