Today I Was Working In My Yard, And Not That

Today I was working in my yard, and not that I know of did I do anything to hurt myself, But I'm hurting really bad behind both knees, and if I stretch my legs at the least trying to go down a set of steps the pain is so bad behind both knees, and now the pain is coming around to the sides of my knees now, kind of feels like my knees are out of joint somehow.