For immediate relief, try prune juice. Drink 8 oz with a bunch of water. Another thing is have some milk of magnesia with a bunch of water.
For every day, drink a little bit of prune juice. Stick with high fiber foods; such as fruit, broccoli, and etc. I have a fruit smoothie with flaxseed every day. Flaxseed is high in omega-3 and fiber, which both are great for pregnant women. Also up your water intake. My dr told me that normally drink 64 oz of water, but with pregnant women it should be almost double.
100 mg colace capsules (generic name docusate sodium) taken once daily with increased water intake. Gentle, safe, non-laxative stool softener. Works wonders. In general, getting some gentle exercise and increasing fiber intake helps a lot to keep things moving as well. I take the Colace every night with my prenatal vitamin and haven't had any trouble with constipation since adding it to my daily regimen.