How can I actually improve?

I've been playing for a few months now and recently I've noticed an improvement in my gameplay, but now I'm getting worse and worse, 3/0 kills up to 8/9 deaths and a lot of assists. I use 2 characters (Yvette and Fuchsia) so I don't get lost in using too many characters, but still I don't understand why after a few days that I actually improved I'm back to where I started... Do you have any advice guys?