Weight up but measurements the same?

Okay I've been trying to not let my weight get to me but I can't help it anymore. The other week my weight jumped 7 lbs in about a week to a week and a half (not quite sure which). The next day it went down 2 lbs, and from last week to this week it went down another lb. But the whole time from before the weight gain to now my measurements have been the same. The only thing that's changed a bit is my bicep measurement is about an inch bigger than last time I remember measuring it (maybe a month ago?) and I can get a couple measurements about 1/4 in. smaller than before. I know muscle weighs more, etc. but an inch on my biceps cannot make me 4 lbs heavier than I'm used to. Does anybody have an idea of what's going on? Could my body be retaining water for some reason? I've upped my intake of it in the past few weeks from around 8 glasses a day to 12. Any help is appreciated!