17 Yr Old Female Chronic Vomiting Every 6 Hours And

17 yr old female chronic vomiting every 6 hours and severe stomach pain. Two episodes within one month lasting 4 days each. brown color vomit. not able to keep down any food or drink during the episodes. has lost 10 percent body weight. Has appointment with Gastroentrologist in 2 days. What next steps should we be sure to take to find out what is wrong?