I am a 17 year old female. I have been dealing with major lack of appetite. I have also been feeling nauseous but I never had thrown up from it. I feel sick when I don't eat and when I do eat, I end up feeling more sick. I have chronic fatigue syndrome and orthostatic intolerance. Any ideas of what this could be. I've been getting told by many to see a GI doctor. What types of test does the GI do to determine what an going on? Anything would be helpful! Thank you