Hello, Every So Often (mostly In The Mornings) My Urine

Hello, every so often (mostly in the mornings) my urine will go from a clear yellow to a milky color toward the end of my tether. I can not only see the change in color, but I can feel the change while urinating, once I am finished it feels as if I hadn't finished urinating. Again this only happens every so often. I am a 21 year old male that is very active, and I drink nothing but water and milk.