I'd say losing focus after a while is normal - when I was doing LNB-attempts I noticed that my best attempts would happen at the beginning of my lengthy playsessions. For 1CC's in particular I also had the problem that as I got more comfortable with dodging all the patterns I also got less willing to bomb which led to dying a lot with bombs in stock. Maybe you're having the same issue?
Don't worry about feeling that you're getting worse. If you're trying something for a long time, chances are on that you're also going to have some bad days just because you statistically have more opportunities to do badly. It might also just be your standards rising - when starting out with something, being bad is normal but if you do well it feels amazing. The more you go on, the more does doing well become normal and when you happen to play lousy it feels like being "worse than you should" and thus really bothering. This can't really be helped in my experience - just stick with it and you'll get it eventually. Seeing how you've stuck with it for a month without giving up you should definitely have the perseverance necessary for this. And perseverance is the only thing that's truly required for those games, after all!
"I know I shouldn't play these games if I'm not good at them" - dear god, reading something like this upsets me every time. Please don't! Everyone who's good at Touhou now got there because of playing the games, even when they were bad. Also, what is bad? There are players who can 1CC some games on Lunatic without even using bombs and still consider themselves "bad". Being in a community is great, comparing yourself to otherwise is nice too, but don't take it too seriously. It's best if you play for having fun.
If you don't see any improvements over some time you can try learning better strategies (quite some hard parts in EoSD can be made absolutely easy with the right strategy). There's no shame in copying strategies from others, watching their replays, searching on YouTube and the like. Trying different shots may help too, if only for being a change when you get bored over trying the same thing for too long.
Question of personal interest - what difficulty are you attempting and what's the farthest you've gotten yet? I wish you all the best of luck; also you may send me a private message if you have specific questions.