What Causes Stabbing Pain In Sternum And Breathlessness?

My daughter has been having stabbing pain in her sternum area, along with this she get very short of breath to the point i think she is going to pass out. This happen once before about 5 months ago, and happen again yesterday and again today. I took her to the ER every time and her ekg(heart test?) is good and blood is normal, also the ultrasound was normal as well. So the dr treated her for esophagus spasms and stomach ach, the other one treated her for asthma, and one of them just treated her stomach. So i have no idea what to do, please help