I have the exact same issue. I can gain up to 5 pounds...then when my body decides to empty...it changes. I do think some of my weight gain has been to eating too much carbs/calories. I've restarted myself to start watching both...hopefully the weight goes back down. I hate the bloated feeling...sometimes my stomach is just huge... I drink 8 glasses or more of water...plus 5 cups of coffee (not sure if that counts...I know cokes don't).
My clothes seem to fit still just because the rest of me is shrinking because of working out...I just wish my weight would show it..