I identify as genderflux, my experience is similar to yours in that I fluctuate between agender and female. I get the exact same doubts, I wonder if I am confused, or if maybe I just want to be special. Sometimes, particularly in the beginning I would convince myself that I was a certain stable gender, be it a cis woman, or a demigirl etc. Then my gender would shift and I would become confused again. I still haven;t stopped doubting, but it is getting less and less. What I didn't expect was how much happier I am, I'm not out really, and I don;t know if I will be. but I guess the difference is in understanding and accepting myself. I changed my presentation, and payed more attention to how I was feeling, and it made a difference. I also feel more comfortable breaking gender norms, wearing the clothes I like, and not behaving in a girly way, when I am not a girl. These things aren't exclusive to being genderflux, but for me they came from having a better understanding of myself.
I think the other thing is that we are pioneers in a way, there are very few people who can tell us what this world feels like, because not too long ago there was no word to describe it.
It is nice to hear from someone else who thinks they may be generflux. because there are so few of us, Good luck in your journey of self discovery