Probably Irritable Bowel Syndrome
Your gall bladder
removal does not have any relation to your current symptoms of abdominal pain
and episodic diarrhea unless the symptoms started following the surgery. If there has been a wide gap of years between surgery and the recent symptoms, the symptoms may be secondary to early stages of Irritable Bowel Syndrome(IBS). Please verify this detail during the follow-up.
I am glad to know that Imodium affords adequate relief. It's one of the medications I commonly use to treat IBS. Though it is ok to use imodium once in a while, I would encourage you consult a gastroenterologist
and undergo a few relevant tests such as stool routine/microscopy and colonoscopy
to exclude infection and inflammatory conditions.
As you plan a gastroenterologist review, I recommend that you modify the diet - add plenty of fibres, avoid large meals especially fatty and spicy ones, avoid all those food that induce symptoms. It may also be better to try antacids for couple of weeks. Prilosec OTC is over the counter available antacid.
Hope I have answered you query.