I have a sharp stabbing pain inbetween my boobs. Literally right in the middle. Made worse by coughing and sitting up. No recent ilness or injury. Why?

Costochondritis. I think you most likely have an inflammation of the cartilage which connects the ribs to the breastbone. It is called costochondritis. It is very painful and the pain can be elicited by pressing the spot where the rib attaches to the breastbone. Treatment includes using anti-inflammatory medications like Ibuprofen and either heat or cold. It resolves over time.