Google says weight can vary almost 3 kilo/5-6 pounds daily.
Things you don’t know until you know.
I recently hit a new low and been tracking my weight throughout the day. Was getting worried every few days as weight seemed to be increasing again forcing me to focus more on lifestyle when I thought was doing well following same routine.
So, not so worried.
Got up in the morning, weighed myself.
Took a pee.
Weighed myself again.
Lost an entire pound.
Next time, weigh yourself before and after a 
following a hot pot dinner.
Each bowel movement for me is at least 0.5kg.
Sleeping consumes energy, so wakeup weight should be less than when you retired for the night. Breakfast will soon recover what you lost.
I would have thought you lose more in water than in “consumed energy” tbh. The latter must be pretty negligible.
That spelling of throughout is killing me
I weigh the least when I wake up after peeing. If I go out for a run, I lose another kilo or so from the sweat, even during the winter. I’m not sure about 3 kilos difference between morning and later afternoon for me, but a 2 kilo difference is definitely common for me.
Also every time I go on a cannabis binge in Thailand I loose my regular status.
Yeah, that’s one of the requirements. No drugs. 
Might go negative.
The only thing I can suggest is: weight yourself at the same time every day, in the same clothes, on the same scale, in the same state. So I weighed myself daily until I got comfortable with the pattern: unclothed, after getting up, before consuming anything as soon as I could see the scale clearly! LOL!
While fluctuation is common, establishing a baseline weight will give you better grounding in how much you actually weigh. And you’ll understand short-term fluctuations more clearly as they relate to your lifestyle.
So for example, after breakfast weights I noted would generally be about 0.4~0.5kgs heavier. I stopped weighing myself after lunch, unless curiosity got the better of me. I was also able to track weight loss more effectively which in itself became a virtuous cycle.