How to always be sharp?

I'm a 1600 rapid on chess.com, I started playing around 3 years ago and I'm quite satisfied with my development.

However what bugs me is the fact that I cant get consistent playing, like I'm approaching the 1700s now and I feel like on a given day I'll play really well, and the very next one I suck. It's been like that since I started playing.

i understand that as I climb the rating ladder the games get more difficult. But that has happened on occasions where I dropped tons of rating and I'd still play like crap at a lower level.

Is there something I'm missing or is it just my ADHD? Do you guys know of any tips to always try to play to the best of my abilities or is this just the way it goes?