Under my left breast bone it’s tender like a bruised feeling. No marks on skin. When I cough/sneeze it hurts a lot in that area. Over a week now.

Chest muscle strain. from coughing. If pain is severe you will need a chest x-ray and exam; otherwise, use ibuprofen ( Advil) or naproxyn sodium ( Aleve) assuming that you are not allergic to NSAIDS or any of these medications.
Cough. Cough has several causes, and if it persists or interferes with breathing please see your physician. Keep nasal passages clear with saline or a decongestant.