I Am A 51 Yr. Old Female I Suffer From

I am a 51 yr. old female I suffer from GERD. I have been having pain in my lower right abdomen, directly below my right rib cage. It seems to get worse when I eat excessively, or after having an alcoholic beverage. I also have irregular bowel habits, even though I eat a wide variety of foods. I have been drinking Diet Coke in excess, and wonder if the combo is causing the great discomfort. I had pizza and soda for lunch, and have been miserable ever since. I just drank some peppermint tea, due to nausea with this symptom and took pepto, but nothing seems to help. I take a Prilosec every morning. Please advise...Thanks!