Is there a reason it hurts under my shoulder blade when i lay down?

Multiple Things: Many sources can result in referred pain to the shoulder blade. Along with the neurogenic sources like cervical (c6 for example) and the suprascapular nerve, we also see many patients with occult shoulder pathology have referred pain to this area. Patients who are very flexible can also have occult shoulder instability refer pain to this area. http://www.theshouldercenter.com/shoulder-pain.htm.