I had no alternative but to do so.
I should have done that.
I had to shop.
I should have done so too.
しなきゃよかったな。
You should really have done it (for) yourself.
I should have been careful!
I had to do everything alone.
I wasn't supposed to become a nurse.
I should have said.
It just turned out that I had to do it.
had to boil the contaminated water