My name is Metta and I am a scale-o-holic. And my weight fluctuates a lot like yours, too. And, like you, because I'm making a lot of progress with fitness stuff, I think I'm gaining muscle.
I've been a lot better lately. A few things have changed. I quit recording my weight every day. I was using one of those LilySlim trackers. I decided to record only once a week. I still weigh myself daily, but it has less "charge" and I can't tell you - down to the ounce - what my exact weight is day to day. I used to be able to recite it for the past ten days. I also changed my goals so that it's not a weight-dependent thing. And when I sense my clothes feel different, instead of running to the scale to see if that means there's been another ounce lost, I just relish the moment. Okay, I tend to relish for a good bit of the day, frankly.
I don't think there's a cure for scale-a-holism, but you can help the symptoms.