What is this weight I'm gaining?

I'm 18 years old 183 lbs and 6'3" i recently started a bulk stage lifting and have gained 6 lbs in a week. I weighed myself in the beginning of the week and the second time one week later ( both were before eating breakfast and after using the bathroom). I'm eating about 3200 calories a day and before the stage i was eating about 2000 calories a day ( i was on a cut stage to get lean for summer). I haven't really gained any inches on my waist line (there is always a small fluxuation) and my abs look the same as they did before at the beginning of the week. I dont think i've gained any fat but i know i can only gain .5 lbs of muscle per week. So my question is what is the 6 lbs that i've gained in a week actually? Any answer is appreciated and an explanation is even better. Again i dont think its fat because it doesn't look like i've gained 6lbs, but any help is appreciated. thanks