probably water retention & lack of movement/exercise. I guess you'll experience a lot of minor weight changes on your journey to a healthier lifestyle. Some weeks, maybe even months you may go up slightly on the pounds, but as long as you stick to your exercise & eating routine, the weight will come off.
I have lost 30 pounds over the past 3 years. And I am still losing it. Just.. sticking with your regime & giving yourself time off while your sick will help you a lot more in the long run. :)