Hi, how many days of illness is it? How severe was the infection? Did he require hospitalisation? Your brother is young and assuming that he has no other health issues like diabetes and hypertension, this symptom may be musculskeletal pain(related to muscle bone in chest wall) or part of post Covid fatigue aches and pains, called post viral myalgia.  If his D dimer is normal and he has recovered, then nothing to worry. CRP elevation is due to the Covid infection and is expected. As long as it is showing decreasing trend on repeating, don't worry