When abdominal pain is chronic and unremitting, with minimal or no relationship to eating or bowel function but often with a relationship to posture (i.e., lying, sitting, standing), the abdominal wall should be suspected as the source of pain.
This can be related with cutaneous nerve root irritation, or trigger pain point.
Also, lower right abdominal pain , that feels like cramps, can be due to constipation (intestines wall contracts in purpose to move the hard stool)
These cramps usually last for 10 to 30 minutes.
If you don't find laxatives helpful, you may have a fecal impaction, that can be removed only by performing colon irrigation.
As your doctor suspected, you may have a constipation form of IBS, irritable bowel symdrome.
One of the complications following umbilical hernia repair, is chronic lower abdominal pain due to injury of nerves during surgery.
One other thing that needs to be taken in consideration, are adhesions, or fibrous scar tissue bands that form after almost all abdominal surgeries.
The adhesions form on abdominal organs, causing them to stick to one another or to the wall of the abdomen.
This can lead to intestine obstruction with symptoms of severe, crampy abdominal pain, abdominal swelling, nausea or vomiting, inability to pass gas and stools.

Best wishes!
Marija