Should I go to a doctor about my knee?

My knee has been hurt for just over a year and has not healed but has gotten worse over time. I can bend my knee but sometimes if I walk to much, it hurts. If I kneel on it, it really hurts. I got knocked over and fell really hard on my knee in high school in the hall. I'm not athletic and I don't have bad knees. There is something in my knee that moves and isn't supposed to. My knee is swollen and bruised. What might I have injured and should I go see a doctor?