:0( That's annoying. I weigh daily and can see large variations in response to quite minor infringements of my low carb rules. Any idea what caused it?
If, by infringements you mean you've had a few extra carbs, I can have a stab at it. Many carbs carry water through our systems, to aid digestion and well,.......... onward transit. The opposite is part of the reason when we low carb, there's often an impressive amount of weight lost very quickly, hen it stabilises into a more usual pattern.
Another consideration could be, that on a given day, or the previous day you have plain old eaten a lot - even a mound of low calorie vegetables and to be as delicate as I can it's still going through the system.
I trimmed up and have maintained my weight for over 2 years now. In my routine, I step-on/step-off the scales every morning and although my core weight is rock solid I can go a couple of pounds/a kilo either way on that. I don't consider that range to be a real gain or loss of weight.
For women there can also be hormonal considerations. Our hormones can promote water retention at certain times of the menstrual cycle, just for an added irritation.
Just stick with it. Variations happen in everything in our lives.