I am a sweat-monster. On my longer rides (maybe 50 miles or so) I generally drink 2 big bottles of Clif and 1 or 2 cans of Coke or a latte. (or a beer or 2 or 3.... TE rides to the RedHook Brewery!) Even in the cool Seattle weather I will sweat through my clothes and get crusty salty skin.
Weird as it may sound, plain water and I don't get along well on rides and if I drink too much my stomach gets oooky.
Maybe you pounded down too much water?
Retaining 4 pounds worth of water during a ride is pretty impressive! If you go by the ol' "a pint is a pound", you were retaining about a half gallon!
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson