I always try to go to bed earlier but I never do, so I'm behind on my sleep.
I haven't been getting enough sleep lately because I don't go to bed early enough.
この場合、次のような言い方ができます。
ーI always try to go to bed earlier but I never do, so I'm behind on my sleep.
「いつももっと早く寝ようとするけど寝れなくて、寝不足だ」
to be behind on one's sleep で「寝不足である」と言えます。
ーI haven't been getting enough sleep lately because I don't go to bed early enough.
「遅くまで起きているので、寝不足だ」
to not get enough sleep で「寝不足である」とも言えます。
ご参考まで！
I know I have to go to bed early, but I'm sleep deprived.
"早く寝なきゃとは思っているけど、寝不足"
- I know I have to go to bed early, but I'm sleep deprived.
早く寝ようとしているがなかなかできない。そして、毎日寝不足です。
- I'm trying to go to sleep earlier but I'm not able to do so. So, every day I don't get enough sleep.
カナダ 
アメリカ合衆国 
