You went out, had a few foods with salt in them and a bit more in the way of carbs than usual. This means your body holds on to a bit more water and there's probably a bit more moving through your digestive system.
Actually going out and moving more for a weekend works the muscles and, in order to heal, they hold on to a little bit more water, especially if you've also been doing a lot of physical stuff in the week leading up to that as well.
You've then come back to warmer weather and are likely not drinking a great deal of water or consuming foods with a higher water content, like vegetables.
Add into that you're perimenopausal and your periods are likely to be a bit over the place, so you could be due on, which also makes it more likely to have a bit of water retention.
Whilst doing some form of exercise is important, especially when dieting (never mind what sounds like it was crash dieting), that doesn't mean you need to go out and buy a bunch of weights on top of any other large exercise equipment you already have. Just moving is enough to start with.
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I want to add to that 4lbs is just over a quarter of a stone, not half, and digital scales can show a different weight within a minute of standing on them due to them being moved, needing charging, you standing on them slightly differently or just absolutely randomly.
Odds are if you wait until Monday or next Wednesday to stand on them again, if you eat the way you normally do - which does not mean fasting - it'll be back to the usual number, as your muscles will have healed, you won't have so much salt intake, you'll have had some sleep and been to the toilet a few times and you may have had your period start. And if it doesn't next week, carry on doing the same and it'll be the week after that.
There is no benefit in having a go at yourself about a tiny fluctuation that will probably be gone before the Bank Holiday Weekend.