I have been having sudden sharp severe pain in my sternum multiple times a day. it gets worse with movement and breathing. it feels heavy, and i have also been coughing a little. any ideas what it is?

Some ideas: The sternum & its surrounding pivot points with the ribs will occasionally become the site of an inflammatory process. This can be isolated or a reaction to a prior cold or other viral infection. Anti- inflammatory agents like ibuprofen can help some as may a cool compress. If the pain is deeper it could be related to the lung lining near that site. An exam may help sort it out.