Perhaps it was the chicken. I doubt it's Dr. Pepper unless you drank too much of it. Most likely either the cooks at the back didn't do it right, outdated chicken etc. One must eat a good chicken. If not they will get this:
Reminds me of the time I ordered a fish dinner delivered from a restaurant before going on a flight. The fish tasted funny but I ate it anyways. As the plane reached half-way to our flight, I had an awful stomachache that I had to horde the plane's restroom a lot of times. It didn't stop there. It went through a whole day until I had a moment with our hotel room's restroom.