my knee hurts when i bend it?!

hey, the same thing happened to me.
I went to my doctors and had it checked out [so i would advise you as well] turns out even though i'm 17 i was diagnosed with osteoporosis - which is when the cartilage wears out! It requires for you to have antibiotics, paracetemol and if it isn't better within 3 months an operation.

So yeah i'd go and get it checked out, safe to be on the safe side!

experience!