What causes diarrhea and vomiting after consuming expired food items?

Hello doctor,

A few weeks ago I was bloated and felt pain in my sides and the pain sometimes moved to my stomach, sometimes my back and bladder. I went to my doctor and he thought I had a UTI and he prescribed me Cipro 250 mg. I finished the course. A day after it happened to me without knowing that I ate an expressed milk chocolate and it expired four months ago. Two days later I had diarrhea. Then the second day it was vomiting and diarrhea and it continued for four days some days diarrhea and sometimes nausea pain and vomiting. My throat was hurting as well which maybe I thought that's why I was vomiting. It is day five and my stomach doesn't hurt, I was feeling nauseous but after I ate I felt better. I still have diarrhea and now I am back to being constipated after eating hard food. I was on a soft diet when I developed these symptoms and had no problem with constipation. But I did not know I was gonna get better if I did not eat hard food. I was also prescribed Dexliant for stomach acid and Phenergan for nausea. What are all these symptoms leading to? Please help.