Remember, weight loss is not linear.
What happens is, your body utilises the fat in your fat cells, and these fat cells fill with water. Some time later, the water gets flushed out of the fat cell and the fat cell collapses.
Lots of things also contribute to fluctuating weight, for example, the amount of salt you have consumed impacts the nephrons in your kidneys, dictating how much water you retain. If you have had a period of not eating very much, then have a good meal, the glycogen stores in your liver replenish, also causing a gain. How full your bladder and bowels are will also impact your weight.
For example, my lowest weight in the past 2 weeks was 16st 12.5lb on 8/10. Today I weight 16st 13.8lb. Yesterday I had a bad POTS day, so consumed a lot of salt. My blood volume is therefore higher due to the impact on kidneys that I spoke about above. I haven't "gained weight". It's likely that over the next 2 or 3 days I will suddenly drop weight again, and I will probably weigh 16st 10lb to 16st 11lb in the next 7 days, because my weight loss trajectory is 7lb a month. I weighed 17st 0.8lb on 01/10 so I expect to weigh around 16st 7 or 16st 8 around 01/11.
I hope that explains things a bit?!??