You are not experiencing fluctuations in your body fat, you are seeing fluctuations in your body weight. Two very different things!
A person's daily weight fluctuations do not reflect the amount of fat their body adds or removes. Fat is added or removed slowly and gradually.
What you are experiencing is your body working naturally balancing water, muscle, food, etc.
Also, bathroom scale readings for the same weight will vary due to humidity and heat.
Daily weight readings are incapable of showing pure fat loss and gain, and there will always be a range of error of up to one kilo either side of your "real weight" depending on daily weight due to water, food and variable scale readings.
So, use weight readings as a guide over time. If your weight wobbles up and down slightly but gradually moves lower over a few weeks, then you are doing fine.