I'd like to know what tense should be used in this case.
My father had an operation in March.
1) Since I had to take care of him, I hadn't worked for 6 months.
2) Since I had to take care of him, I didn't word for 6 months.
Now he got better, I will start working from next month.
Which tense is appropriate 1) or 2)?
It suggests that 'since' here has a meaning of 'because' as the time phrase fulfills that, so I'd say:
Since/because I've had to take care of him, I haven't worked for 6 months.