This used to happen to me for a few years on and off. Maybe it still happens, but I no longer use a scale ever. I concluded in the end that it was because of my bowel issues….that sounds gross and is gross, but I used to suffer from constipation a lot, so if I didn’t poop for a couple days….it makes sense that I would be quite a few pounds heavier than if I was pooping normally. Is this at all the case with you? It’s the only thing that made sense to explain it for me, but I could have been totally wrong too. I never went to a doctor and asked since the issue resolved on its own. Hallelujah Mary.