Translation of "Frustrating" in Japanese

Found it a bitter and frustrating experience.

それが苦くて苛立たしい経験であることに 気づき

And that was very frustrating at first, so difficult to discern.

‎最初は見分けがつかず ‎もどかしかった

During the advance into Russia, Murat’s  cavalry faced a difficult and frustrating task,  

ロシアへの進出中に、ムラトの騎兵隊は 、広大な風景の中で敵を見つけようとして

Ah! It's so frustrating not being able to keep up with everyone else.

あっ。みんなについていけない。イライラする！