Getting enough fiber but having a hard time using the bathroom today.?

I have been particularly watching my fiber lately because I was having trouble going to the bathroom for a couple of weeks last month. For 2 weeks now I have been eating the right amount of fiber every single day. It got into my system and I was able to use the restroom just fine, sometimes twice a day. Suddenly today when I woke up and went, it was like pebbles and it hurt! What could have changed over night?