Son, 35, has mild ruq discomfort for over a year, doc did physical exam/ urine test & blood work, all perfect, no effect from food, thin, dont smoke or drink, exercised while life & ate good. no other symptoms, what could it be? very worried?

In general work up continues with imaging studies, such as ultrasound or CT scan, if cause believed to be visceral. In many cases pain proves to be musculoskeletal or functional/ caused by spasm for example and that is not diagnosed with imaging studies. Keeping the same doc involved should help (primary care doc or gastroenterologist), a log of symptoms including type of food and exercise helps.