What Causes Vomiting, Abdominal Pain And Excessive Weight Loss?

I have a question on behalf of my mother who is current suffering from extreme GI symptoms. She has been to multiple appointments with physicians and has yet to receive an answer to what is going on. The doctors she has seen seem totally baffled as to what is going on. For a couple or so months now she has slowly started losing weight and has been unable to eat. Gradually her symptoms worsened and some days she can barely keep down water. She is having extreme pain in her abdominal area and it even progresses to her back. She is unable to eat and is completely miserable. I know this could be on a broad spectrum of diagnosis but is there any way you could tell me what may be wrong with her? Thanks in advance.