now I was the cook

A little context might be helpful with this one.

Well, it is a single sentence appeared as an example in a linguistic book, which attempts to compare Japanese with English.

It has no meaning without context, so your book is a very silly book.

It's the sort of sentence that would be used by someone who has been cooked for all their lives, then they find themselves in a situation where they have to cook.

This is not the only instance it could be used, but I've not got enough time to go through them all.

Somebody might use a phrase starting "Now I was..." when they were writing or talking about a time or period or situation when they had had a reversal or change of roles, literal or metaphorical:

Then I was a passenger, now I was the driver.
Before, I had been a kitchen assistant, now I was the cook.
On January 7th , my job changed. Before, I had been an assistant, now I was the boss.
Before, I had been a boy, now I was a man.

I believe u need some conjunctions in there,
to avoid run-on sentences; i.e., 2 sentences combined into 1
by erroneous punctuation.

Semi;colons will do.

Yes - I was thinking this myself.

Contrex: Yes - I was thinking this myself.

You are taking liberties that are not in evidence.