Hey Im 16 And For Several Years My Knees Have

Hey im 16 and for several years my knees have been bothering me. When I play sports, go for walks, or do anything active for a long period of time it hurts emensely. In the beginning of the year a friend was messing around with me so I went to sit down and she pulled the chair from under me. Since then I had very bad back problems. My hips then started hurting also, I don't know if its because of my back or my knees. But if my family and I go for walks, after awhile they tell me I'm starting to walk weird. By back is always in pain and I don't know what happened to it when my friend did that but it hurt horribly when that happened. My parents think I might have arthritis but they say it may not be because of how young I am.