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The Nur-Isterate can last sometimes 6-9 months before you resume having normal periods, that is probably why it is taking so long for you to have your ovulation and conception.
However please do not worry it will not cause infertility
and you need not take any specific medicines for regaining your ovulation . With time the effect of the contraceptive
will wear off from your system and you will conceive as per your wish.
Also it would be advisable to consult your gynaecologist for ruling out any other problems like uterine or ovarian disorders if you are unable to conceive after 6-9 months of nur isterate.
Hope I have answered your query.