Thank you very much for your question. Pain after a trauma is not uncommon but can have many different potential causes. I suggest that you speak with your doctor
to better describe your pain, quality (dull vs. sharp), severity, duration, alleviating or aggravating factors, and associated symptoms. The exact mechanism in which you got hit can also provide clues about potential causes on the pain you are experiencing.
The area you are describing has skin, muscle, ribs, heart, and lungs in the area. Often times after a direct trauma, you may develop bruising or bleeding
. If bleeding occurs in the skin or muscle, it can lead to a hematoma (collection of blood) that can be painful. You may also have sustained general bruising to your intercostal muscles (the muscles between your ribs that can assist with breathing). Another possibility is that you may have fractured a rib. This can manifest as pain on palpation, with breathing, or with movement. This can also alter the way in which you breath which can affect your back and shoulders as well.
It is not possible to receive a diagnosis without being evaluated by a physician. I suggest that you make an appointment with your doctor or local health center.