I agree that even one day without a BM while pregnant is cause for concern, and suggest that if your bowels have not moved by bedtime to take a 3-4 pint gentle cleansing enema for immediate relief.
You can take enemas as often as desired during pregnancy, daily if necessary, to provide relief. But don't use the chemical pre-packaged disposable units sold in supermarkets and pharmacies, use an old fashioned enema bag.