The Past Perfect Continuous: Meaning

To emphasize an action that was in progress before another action, or time, in the past.

Sally had been working in her new job for two weeks when she found out she was pregnant

The Past Perfect Continuous: Forms

Affirmative (Positive)

They had been working all day when the boss arrived.

Form: Subject + had + been + verb (ing)

Negative

I hadn’t been working for long.

Form: Subject + had + not + been + verb (ing)

Question (Interrogative) 

What had you been doing all day before I called?

Form: Had + subject + been + verb (ing)?