I have a dull ache in my left shoulder blade but when i take a deep breath or move a certain way it becomes severe. only started this morning?

Could be serious: Any pain in the chest region that gets worse with deep breathing is suspicious for a blood clot. You are young and female, so if you are on OCPs or have traveled recently in a sitting position, you should be checked for that, promptly. However, movement associated pain usually means muscular injury, so for example a recent unusual or prolonged activity using your left arm could have set it off.