Knee Injury from car accident

I am 16 years old and was in a car accident. I hurt the right side of my body. I was treated for my injuries such as my rotator cuff injury and my open ankle fracture. They said my knee was just sprained. It has been 8 months since the accident and my knee is still swollen and feels like it is going to give way when i run. All my other injuries have healed well though. I went for my checkup and my doctor said nothing was wrong. What should i do?