Soda causing diarrhea? News to me. Usually when I drank milk my shit was more liquid, while it was the opposite for coke.
It is probably the caffeine. Caffeinated soda dehydrates you. It gives me the runs too.
Speaking of, my day was similar to the OP's. I got really sick and was squirting and puking at the same time for hours. It was pretty uncontrollable. Because I recently had a kidney transplant, my transplant team had me go to the ER. I thought I was going to shit myself on the drive over. Was there for about 5 hours before being discharged. Kidney is OK thankfully, but I still don't feel great.