hormones and diurisis what fun! On top of your body getting rid of all the extra fluid that it needed when you were cooking your sweet boy you were probably also pumped full of IV fluids. I think this is natures way of giving us a taste of hot flashes and night sweats. I recall hubby waking up wet and wondering what the hell was happening, between sweat, baby urine, the first new poops and breastmilk it was quite an experience!
Also if they havn't told you, sometimes with boys you can see salmon colored streaks in their diapers, your probably past this point now, but my first, a boy, also a whopper(10.3) had this and no one had told me about it, it's crystalised uric acid that they are clearing out of their urinary tract the first few days. Ahhhh, the science lessons are endless.