Is this why I gained weight?

First of all, big hugs, it's not fun watching the scale bounce up and down especially when you have issues with control!

Just wanted to share my own recent experience to help you get some perspective on how much variance is normal. I weigh myself at night and in the morning - I'm a diabetic so I just step on the scale at the same time I'm taking my blood - but only officially update my weight once per month. I'm in maintenance right now and consider my "official" weight to be within a couple of pounds of 149.

On New Year's Eve slept in late and as a result woke up slightly more dehydrated than usual, weighing 146.6.

That day was a rest day from working out, so no muscle swelling from exercise, but I did eat a lot of rich food, as a result -

New Year's Day - Woke up at 151.4.

That day ate lots of black eyed peas with ham and greens and cornbread, ran 8 miles, had muscle swelling from exercise plus bloating from sodium, weighed 156.2 before bed.

Jan 2 - woke up at 152.4. Did a strength workout, but ate less sodium.

Jan 3 - woke up at 151.0. Did another run, very exhausting trail run, ate ALL the peanuts at five guy's.

Jan 4 - as a result of way too much sodium and needing a rest day, visibly puffy and back up to 152.4.

Took a rest day, ate lots of veggies.

Jan 5 - woke up at 149.4.

So in one week, my highest weight, bedtime after a sodium-filled day of exercise, was 156.2, and my lowest weight, morning after sleeping in late, eating moderately the day before, and using the bathroom, was 146.6 - almost a ten pound difference. During the whole week I ate at maintenance calories after accounting for exercise. My actual body composition? Probably did not change at all! I expect I will see 147 again soon, and 152 again soon. Those are part of my natural fluctuations, even when I weigh myself first thing in the morning.