My son for 2 weeks been exhausted,fatigue,nauseous when sitting up and physical activity breathing problems.neg for covid. plus body aches. no fever or cough?

This could be other viral problems or even cardiac. Make sure to support with good fluid intake and diet in the meantime and if viral often gets better within a few weeks, otherwise needs some labs and a chest xray.

I agree that this could be a viral infection which is self limited. You don't mention your son's age. Nevertheless I feel his symptoms persisting 2 weeks warrant an evaluation by a physician at this time. Has he been exposed to anyone with Covid in the recent past? Lack of fever is somewhat against his having Covid, but I wouldn't postpone his medical workup.