Brief stabbing pains in left breast/chest. some left should blade pain. doc says heart is fine. muscular?

Probably: Such pain is usually musculoskeletal. Other telltale features confirming this are palpable tenderness over the affected area, accentuation of the discomfort when changing body positions such as rolling over in bed. If the pain is accentuated by deep inhaling, is accompanied by fevers, sweating, or palpitations then probably needs further checking out.