Well since your doctor wants that you get periods soon ,she has given norethisterone
so that you will have periods (withdrawal bleeding) and she can start medicine for IVF. But i suppose ,you are fearing you might be pregnant and norethisterone might affect your pregnancy
if your are so. Well in that case I think it will be better if you menses to start naturally so that you can start your drugs for IVF.The problem is if your infertility
centre does IVF in batches then the menses of all the women undergoing IVF should be at a same or nearby dates and it might be a concern for gynecologist. In that case you may post pone IVF in the coming month and take it up in the subsequent month. YOU can start a combined pill next month and continue it till your doctor says you so that you can schedule your cycle.
I suppose I cleared your doubts.
good luck ,bye