"I was really busy at work for two weeks until yesterday."
"I was really busy at work for two weeks until yesterday."
"I was really busy" 「とても忙しかった」"swamped" も言えます。
"at work”「仕事で」
"for two weeks" 「二週間」
"until yesterday" 「昨日まで」
[これも](https://eikaiwa.dmm.com/uknow/questions/6108/)役に立つかもしれませんので是非クリックしてください。
I've been very busy at work for the last two weeks right up until yesterday.
この場合、次のように言えますよ。
ーI've been very busy at work for the last two weeks right up until yesterday.
「この2週間、昨日まで仕事ですごく忙しかった」
for the last two weeks「この2週間」
right up until yesterday「昨日までずっと」
ご参考まで!