YOU SAID:

You've only been in Japan for a few days.

INTO JAPANESE

あなたは日本に来てまだ数日しか経っていません。

BACK INTO ENGLISH

It's only been a few days since you came to Japan.

INTO JAPANESE

あなたが日本に来てからまだ数日しか経っていません。

BACK INTO ENGLISH

It's only been a few days since you came to Japan.