I had covid during january. had none stop coughing and had lasting pain in rib area after coughing. eventually after 5 weeks went away. had a powerful sneeze and his pain is back after i felt a pop.could it be a fracture or is it caused by cancer etc?

The only way to find out what's going on is to be fully examined. Chance of cancer relatively small. Go see your GP.

Chest wall musculoskeletal pain is a likely cause. The COVID infection and associated coughing may have inflamed the chest wall. The sneeze causes muscular strain and most likely muscular pain. A local heating pad is often useful in providing relief. Watch for return of COVID symptoms, discuss a COVID vaccination with your PCP and rest. IF pain continues, please see your PCP.