You are probably indeed being a bit over critical, becuase what you have shared so far is pretty good! And more importantly, I think there is clear improvement if you look at your journey so far.
But as Marc has also said, don't force it, take a break if you feel frustrated, stop when you are at a drawing high, overall we need to keep ourselves motivated and enjoying this.
If by any chance you haven't seen this video, it's a good watch!
I struggle with colors a lot myself too, it feels like I make a mess whenever I try to get "creative" and am at my best when I just take colors from references (which feels kind of disappointing to myself). Still, it's part of the learning process to build a mental library, and I'm convinced that includes color combinations.
For example, these envrionment pieces look amazing. The shades and warm colors highlighted by a bit of blue on the warmup. And as someone who has struggled to make organic looking rocks, that exercice looks pretty good.
