Why did I put on weight???

I have been weighing myself daily contraversial I know! But, I want to understand my body and what the hell goes on with it and I believe that weighing daily is important. Let's take today as an example... I put on 2lb! Virtually impossible one would have thought considering my current diet but nevertheless 2lb I put on. This is my weight loss thus far...

Day 1. 21 stone and 5 pounds (start weight)
Day 2. 21 stone and 2 pounds (3lb loss overall)
Day 3. 20 stone and 13 pounds (6lb loss overall)
Day 4. 20 stone and 12 pounds ( 7lb loss overall)
Day 5. 20 stone and 10 pounds ( 9lb loss overall)
Day 6. 20 stone and 10 pounds (9lb loss overall)
Day 7. 20 stone and 10 pounds (9lb loss overall)
Day 8. 20 stone and 11 pounds (8lb loss overall)
Day 9. Not weighed as op day
Day 10. 20 stone and 8lb (11lb loss overall)
Day 11. 20 stone and 8lb (11lb loss overall)
Day 12. 20 stone and 10lb (9lb loss overall)

So, did I panic? No! I am begining to understand weight loss as 'ebb and flow' and even though daily weight will show fluctuation, weekly weight should be more stable in terms of loss. The first week, I lost 8lb and this week, I expect to lose about 5lb due to 'slow down' and increase in calories after op compared to pre op diet of 850 cals per day. We shall see!