My fiancee had the same trouble with constipation. We finally figured out it was B12 anemia. You could try some B12 supplement and see if that helps (if you haven't already tried that, of course).
Here's another possibility for you to consider: Before this did you take anything to help you go to the bathroom? The reason I ask is because taking too much of a constipation-relieving supplement can make your body addicted to it. Then your body may have trouble going to the bathroom on its own.