What Causes Breathing Difficulty With Good Oxygen Percentage?

Hi my name is Joe and my Daughter Sandra has a Respetory problems we just got back from the hospital and the doctor said there is nothing wrong with her, her oxygen is at 100% its good all her vitals are good but her breathing really is bad and I worry so much, it sounds like there is something in her throat and nose it s sounds like very little air is going in i have taking her to other doctors and they can t find anything wrong with her don t know what to do.