Hello~Sounds muscular to me, I would certainly see your doctor and gets his/her opinion on this matter. I always feel like anything remotely pertaining to the heart and pain should be looked into.
I don't think that's normal, I have never gotten pain from yawning. Have you talked to a doctor about it? Maybe you have some sort of cyst or abnormality causing pain, or maybe it's muscular. You also open up your lungs by yawning, so maybe it's related to your lungs.