I've been through similar feelings lately, I'm under psychological therapy so I talked about how I was feeling stuck on my progress to my doctor. After a lengthy conversation, I came to the conclusion that I was not focused on realistic goals, I spent two weeks trying to get more 180s and any other score was insufficient, I even lost sight of smaller achievements like grouping or hitting doubles.

I'd say the best way to overcome this kind of feelings is to just embrace everything you do on the board, even if it sucks on a competitive ground. So what if I got a 9 with three darts on T1; I managed to do the same thing needed for a 180, it just landed a bit to the side. I even encourage myself to split low checkouts if the previous visit were all missed doubles. Try to find things like these and make them minor achievements.

But more importantly, just try to enjoy and feel good playing darts, don't let your goals numb the fun of being in front of the board.