I have a sharp pain everytime i inhale or move a certain way behind my left rib under my breast for a few days what can it be?

Costrochondritis: Sounds like costrochondritis, an inflammation in your chest wall. However, if you are short of breath or the pain persists, you need to see your doctor.

Be Careful: Dr koreff - wolfe is most likely corrct, but a spontaneous pneumothorax, which is where the lung pops open allowing air into the chest cavitity is a rare possibility, particularly if you are tall and thin. If it persists see your doctor.