Suggest Treatment For Bruises And Swelling On Knee

Hi, My daughter is 13 years old almost 14 and she is in track gymnastics and marching band. She s always had problems with her right knee sometimes her left also. But everytime she goes to a doctor they just take her out if her sport for a few days. & they ve never done an X-ray because they say that it won t show anything. Her knees always have bruises on them & they swell a lot. She also gets lightheaded a lot. I m not sure what to do.