I get really sharp pains in the middle of my chest between my breasts when i yawn or take a really deep breath. any ideas?

Chest pain: You may have costochondritis of the sternum. Taking ibuprofen may reduce your pain

Costochondritis: Costochondritis, also known as "chest wall pain" is an acute and often temporary inflammation of the costal cartilage, the structure which connects each rib to the sternum at the costosternal joint. This area will move with coughing, breathing, deep yawns, etc, and may get painful if indeed inflamed. An NSAID often helps. See the Dr. to be safe!