My dietary plans aren't going as planned. I find myself not being able to resist eating sweets.
I've been trying to improve my eating habits, but it's not quite successful.
ご質問ありがとうございます。
① "My dietary plans aren't going as planned."＝「私の食生活は計画通りに進んでいない。」
"I find myself not being able to resist eating sweets."＝「甘いものを食べることを抵抗できない私がいる。」
② "I've been trying to improve my eating habits,"＝「食習慣を良くしようと努力している」
"but it's not quite successful."＝「でもあまり成功していない。」
ご参考に。
My eating habits have been off lately, and I've been eating more sweets even though I know I shouldn't.
この場合、次のような言い方ができますよ。
ーMy eating habits have been off lately, and I've been eating more sweets even though I know I shouldn't.
「最近食生活が乱れていて、ついつい甘いものを食べてしまう」
eating habits「食生活」
乱れていることは to be off を使って言うと良いでしょう。
ご参考まで！
アメリカ合衆国 
カナダ 
