What Causes A Bump In The Sternum Area Post Treatment For Back Injury?

I just found a bump in the sternum area. Its not painful and I can breathe normal. I just had a back injury on January 30th. I m going through therapy. During therapy I m on my stomach sometimes as they press on back to try and open up the back and also go to a chiro. Could the therapy and chiro be the cause of the bump? Or something else?