A few things-
first, it's not an accurate comparison to weigh yourself before bed and then when you wake up. You're going to be lighter when you first wake up and heavier when you go to bed (you still have a lot of food and water in your body when you go to bed)
secondly, how much are you eating? I started seeing some drop in weight during the 3 week, but I was eating FAR less. I've extended myself to 5 weeks in my cycle because my food intake was so bad for a week and a half (largely outside of my control unfortunately), and I'm shooting back up again now that I'm back to 4k calories a day.
Bottom line- it's most likely food intake.