Son,35,healthy,always skinny w/ultra thin waist,weight lifts since teen,eats healthy,never smoked or drank,experiencing very mild ruq discomfort for months,stays same,no effect from food,what could this be? i'm a wreck he may have something serious?

An evaluation is indicated. His weight lifting may have resulted in muscle strain, but liver disease and other conditions should be considered. If he is otherwise healthy, encourage a healthy diet, sources of lean protein, hydration and avoid excessive weight lifting. Watch for signs of weight loss, fatigue and keep immunizations up to date including Hep B