I don't feel like I'm getting better

I don't feel like I am. For example, when I am doing puzzles and lessons, I am not directly learning something... I'm just sharpening a skill. After I play a game and spot my mistakes, I don't see how it helps. How do you get better and recognize improvement?

You measure improvement little by little. Such as “oh I used to have trouble with this endgame but I converted it pretty smoothly this time” or even something as little as one single move with a nice positional idea.

Hmm. But then, sometimes I play bad and sometimes I play good. When I play bad, does that mean I became worse?

From my perspective, you don't feel that you are getting better, but if you deeply look back a little bit you might see that you improved a bit.