I've been restricting food the past few days and today i had a burger. i then had bad cramping and diarrhea that smells like vomit. why is this?

Gastric dumping: My intuition tells me that it is a combination of things. These include the capacity of your stomach to retain the food and send it to your duodenum in a coordinated way being weakened and then your pancreas cannot process if fast enough to emulsify the fats. Therefore it all goes to the colon and causes gastrointestinal upset. You may be better off with more frequent smaller meals. Stay safe!