It could be: reaction to the sauce, poor food handling, onion sensitivity, too much fat in the meat, difficulty digesting the entire meal. I have that problem with another franchise. My solution is that I would order a plain cheeseburger hot off the grill. However, it has been more than ten years since I have done it. In fact, I no longer purchase fast foods, nor even eat ground meat or dairy products. Your options beyond food selection are to see a doctor or gastroenterologist, see if you are sensitive to certain foods (above mentioned), alter your life plan en re selecting what you ingest. I believe you will make a rational decision about what is best for your health. A painful stomach suggests that the food is not passing through the digestive system fast enough. Think about more plant foods. Those break down easily; whereas meat does not. I know this is a point of contention. I used to eat 32 oz prime beef at one sitting. Afterward, would suffer pain. I had pills for it. My cholesterol is slightly high. I have other problems as well. Take the pain as significant, and follow through to see the cause. Make changes that lead to longevity and better quality of life.