is a progesterone
it is given for irregular bleeding to regularize bleeding.
It is also a contraceptive
so you cant become pregnant while taking norethisterone.
Intermittent bleeding, spotting, breakthrough bleeding
are sideeffects of norethisterone. It will become normal and for the pain in uterine area you can take some anti-spasmodics.
There is nothing to worry about your intermittent spotting unless it is much of a inconvinence to you, you should consult your Gync .