Thank you for the additional information.
There are many different causes of abdominal pain, although most of the common causes of abdominal pain have been excluded by evaluation that has been done to this point.
One of the common causes of chronic abdominal pain cannot be diagnosed by any test, which is irritable bowel syndrome, or IBS. IBS is very common, occurring in about 20-30% of people. It usually does not cause acute, severe pain, but it can do so. It is due to altered muscular activity of the gut, which can be either increased or decreased muscular activity.
In someone with normal diagnostic studies, it is also fairly common to have chronic recurrent abdominal pain because of scarring or adhesions in the abdominal cavity. This most often happens after abdominal surgery, but since your first attack preceded your first abdominal surgery, that would not be a possibility. Scarring or adhesions can also occur after certain infections in the abdomen.
Other issues to consider would be chronic panceatitis, and the usual test for this would be blood tests of the pancreas, such as amylase or lipase. Celiac disease also can cause chronic abdominal pain, and there is a blood test to look for this. Certain metabolic conditions also can cause abdominal pain, such as porphyria or sickle cell anemia, but these usually cause less frequent episode of acute abdominal pain and also usually have other associated symptoms, so are not a common cause of just chronic abdominal pain.
If the above blood tests have been done, then the most likely cause of chronic lower abdominal pain that is associated with bowel movements would be IBS, but scarring/adhesions would also be a possibility.