Why would 35 y/o male,always thin, healthy, exerciser, good eater get minor ruq discomfort for 9 months,never gets worse,no effect from foods,never smoked/drank! scared to go to dr,scared it's liver from covid vax 1 year ago,feel perfect otherwise?

Attempting to diagnose a diffuse discomfort such as this over the internet is not the correct way to approach the issue. Please see a physician for an exam, no need to be scared.

Many times such pain is determined to be musculoskeletal, but visceral origin is always possible. Health related anxiety is likely otherwise and for all reasons seeing his doc would be best.

It is not feasible to provide an opinion without additional history, physical examination may be some tests. It would be prudent to see your doctor to see if you may be depressed. Depression is treatable. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity as tolerated. Drink more water. Wish you good health!