YOU SAID:

Quite a lot has happened since I was away

INTO JAPANESE

私が離れてからかなりのことが起こった

BACK INTO ENGLISH

A lot has happened since I left

INTO JAPANESE

離れてから色々あった

BACK INTO ENGLISH

There have been various things since I left

INTO JAPANESE

離れてから色々ありました

BACK INTO ENGLISH

There have been various things since I left