What Causes Recurring Extreme Pain In Stomach?

I need to know about the stomach pain details. My friend is going through an uncertain stomach problem and he is not able to bear that pain. It happens in a way that he feels acidity and a strong pain in his stomach in middle and sometimes he got fainted because of that pain. Here doctors are not able to understands the thing clearly. And he is taking medicines continously but instead it doesnt work. But it is cleared that this is not Ulcer and Liver is 100% perfect. And once there was blood in his vomiting. And one doctor said he should keep his diet right. But if the problem is diet then whats the sense of taking medicines. He is in serious pain and they are saying he just have to keep his diet good. This doesnt make any sense. Kindly help me before it becomes a critical condition. Please help me.