Deep breath causes chest pain for 2 days. What is this from?

Musculoskeletal. In all likelihood you have an irritated inter-costal nerve or muscle and whenever you take a deep breath and the muscle stretches it hurts. Having said that, it is important that you make sure there is no lung problem going on that is mimicking a strained rib muscle or nerve.
Not clear. Only a medical exam can determine the exact cause of your symptoms. See a doctor.