My back has been hurting for 3 days its right under my right shoulder blade as of today its hard to breath gets worse when i lean my head forward?

Back pain: It could be something musculoskeletal such as a bruised or broken rib or a muscular strain. In this case, you just need to wait it out. However, since you are having trouble breathing, you also need to consider a blood clot in your lung which can often present as back pain. I would recommend getting checked out by your PCP to make sure your vital signs (oxygen sat, blood pressure, HR) are normal.