I have such a rule in my head that if we have "already", "still" or "yet" I am obliged to use Perfect Tenses.
But can these words be used in Past Simple?
I already finished the work (some time in Past, not now)
I didn't learn English yet (some time in Past, not now)
I was still learning English.
And difference will be with:
I had already finished the work
I hadn't learned English yet
I had been still learning English