I Am Getting Pain In My Sternum That Happens After

I am getting pain in my sternum that happens after I eat some restaurant food. The firs time the onset occurred 15-20 minutes or so after eating Persian food (chicken, rice), the second time after eating the leftovers the onset was 2 hours later, and then tonight (after eating brisket, baked beans, baked potato) onset occurred 3 hours later. Always in the center of the chest. It lasts about 3-4 hours and then I am back to normal the next morning. After second episode (May 26), went to an urgent care center. EKG was normal, so was blood pressure and everything else. Have none of the other symptoms normally associated with heart attack. What could this be?