On any given day from morning to night I gain 3-5lbs in food & water, but by morning it's gone. Any time I eat something outside of my current calorie range (high or low) I easily gain/lose 10lbs overnight.

I haven't weighed myself that frequently, but I have recently gone up and down about 5 lbs. I supposed it depends on your circumstances, like how much sodium you have consumed - I think that's what sent me up the 5 lbs in the one week.

I seem to be going through this trend of dropping two, gaining one back the next day... staying the same for a few days and repeating.

I generally weigh myself every day, but I do my best to always have the scale in the same place (same bathroom tile and roughly the same position). I tend to wake up, go pee and then hop on the scale (since that means I'm naked). Saturday's my official weekly weigh in for a group I'm part of so that's when I assess how I've done overall for the week.