Cramping abdominal pain is a symptom of constipation and sign that intestinal wall muscles are contracting hard trying to push further the hard stool.
Since you've found one tablet ineffective, and the manufacturer gives dose range 1 to 3 tablets, it will be good idea to try taking more than one tablet.

Do you use laxatives frequently?
How often do you suffer from constipation?
Do you take food rich in fiber and drink plenty of water daily?