I feel nauseous constantly, but especially after eating. I get very light headed and feel like passing out, and have diahhrea, but am also constipated. I feel like throwing up, but can t. I m 18 years old, and have lost over 15 pounds in the last 5 months. I m worried something bad is happening. I ve gone to my doctor and the ER, but they don t do anything for me. Maybe I m not asking the right questions? Please help, I m tired of feeling gross all the time...