Lower left quadrant pain is not something that is usually associated with having GERD, although bowel habits can change when someone is taking PPIs and that can cause diarrhea or constipation and some discomfort. Lower left pain - depending on a person's age - can be associated with a number of other conditions, one of which is diverticulosis. So if you haven't considered having a colonoscopy done, you might want to talk with your doc about it.