my goodness! you're just a couple days postop and walking around? no pain? no discomfort? what does your doc have you eating? most of us at this point were consuming clear liquids only.
having said all that [well, having asked all those Qs!
] please don't be concerned about this weight gain. yes, it does seem weird, but your body has been through some pretty extensive surgery and has probably just about cleared out the anesthesia. give it a few more days - be sure to get your rest - and when you see the doc next week, see what happens! and talk with your surgeon with any Qs you have in the meantime.
the important thing right now is to drink your fluids and get some rest.