Hi I Am A Male And 30 Years Old, Recently

Hi i am a male and 30 years old, recently i did a juice fast it ended Tuesday and today is Thursday, I ate regular food tuesday and wednesday with no problem.

When i woke up today i had sex with my GF and then went to the restroom and made a bowel movement and then suddenly my stomach started cramping horribly. I took a shower hoping the heat would help but it didn't i drank some water then ate 4 spoonfuls of oatmeal and drank more water but then i had to run to the restroom to vomit i emptied my stomach of water, food and bile and then sat there for 20 mins before i started to feel better any idea why this happened?