Thank you for the additional information.
Slow motility of the stomach and gastroparesis would not cause left sided abdominal pain. But it is possible that there can be pain in the left side of the abdomen from either decreased or increased motility in the colon, which also can be causing the constipation. The formal term for this is irritable bowel syndrome, or IBS. There is an increased incidence of IBS in people with gastroparesis. Unfortunately, unlike the stomach, there is no good test to directly measure the motility of the colon. Therefore, a diagnosis of IBS is usually dependent upon excluding other possible causes of the pain.
Other possible causes of left sided abdominal pain would include other conditions of the colon, such as inflammatory bowel disease, conditions of the kidneys, such as infection or stones, or conditions of the female genital tract, such as infection or ovarian cysts.
Although a CT scan would detect many of these conditions, a complete evaluation would also involve a colonoscopy and a pelvic ultrasound (the CT scan does not show the pelvis well). There also should be urine lab tests done to exclude infection or signs of kidney inflammation. If these tests are normal, then that would support the diagnosis of IBS.
Another option would be to manage it as IBS and see if the symptoms improve. The Donnatal is one of the medicines that can be used for IBS. Another common intervention
would be to increase the amount of fiber intake, either in the diet or via fiber supplements. The goal would be to increase the amount of fiber to 25 - 35 grams per day. The average American diet is about half this amount. The fiber also works better if there is also an increase in water intake, as the fiber absorbs some of the water to be effective in the colon. The goal would be to drink eight 8-oz glasses of water per day.
If I can provide any further information, please let me know.