There’s no way you didn’t lose being without food for 7 days. Your period is probably the culprit. You are probably retaining all the water you drank and will see a big drop in a day or so. Just don’t go overboard on eating.
Hormones would be my first thought, if your experiencing PMS or suffer from endometriosis or similar this weight loss is normal. I’ve gained weight during fasting with PMS before, it for me comes off extremely quick following and it’ll even out to the same weight loss I saw prior.