Hi dr, i have a sharp pain on my back and front underneath the rib cage, it's painfull to breath especially deep breath. what could be the cause?

Pinched nerve: Assuming there has been no recent rib cage injury and If the pain us very sharp, fleeting and brought on by a deep breath, it is probably due to a pinched intercostal nerve that runs between 2 ribs. These tend to resolve after a few days, but if they don't or if symptoms worsen, see your physician. In the meantime avoid activities that strain or stress the rib cage.