When i yawn, i get a very sharp pain in my chest. is this normal?

Almost certainly: During a yawn the chest wall expands which stretches many of the muscles connected to the chest wall. If these muscles are irritated or strained (particularly the intercostal muscles that sit between the ribs) you will experience a sharp pain.

Muscle spasms?: Most likely a muscle spasm from the sudden and very deep breath related to yawning ...