Why does my weight fluctuate so much?

Right now I weigh 130. The past month or so it’s been about 130 exactly every time I’ve checked. However, before that, I would be 125, then 130 the next week, then 120…I got as low as 108 and as high as 140 but the thing is my clothes always fit almost the same even though somehow there was a 30 pound difference there ultimately. I was never sick and I never felt bad, but my weight was all over the place. I used the same 2 scales each time and they always gave me the same weight, so I don’t think it was just a bad scale. I’ve been curious about this though. Any ideas?